The latest research into termite foraging behaviour looks into the role of the each caste and answers questions about preferential food sources and transportation methods.
Latest termite foraging research
How do termites forage?
As termite activity is largely hidden in the field, laboratory studies are often the best way to investigate the foraging behaviour of termites, although it is important to remember the results may not always be replicated in the field. Nevertheless, over the years, researchers have built up a solid basic understanding of termite foraging behaviour.
Nasutitermes corniger (pictured above) provides an example. Researchers have described three phases of the foraging behaviour for N. corniger. The first phase is an exploratory phase, when soldiers leave the nest to find potential food sources. On finding a source, they lay a pheromone trail as they return to the nest. The second phase involves workers following the trail to the food source, collecting food and reinforcing the pheromone trail as they return to the nest. The third phase includes intensification of foraging and the building of tunnels over these foraging tracks.
Researchers have recently discovered that the salivary gland has an impact on the workers’ foraging behaviour.1 Comparing salivary gland extracts on filter paper with filter papers dosed with distilled water, significantly higher number of workers were recruited to the filter paper with salivary gland extract and exhibited higher levels of gnawing. However, soldiers did not appear to be affected by the salivary gland extracts. The researchers concluded that the salivary glands of late instar workers contained substances with arresting and/or phagostimulating properties, and that the deposition of these substances at feeding sites would allow these older workers to direct the foraging effort. Similar effects have been seen in other species. If the chemicals that stimulate this behaviour can be identified, they may have a role to play in improving the performance of termite baits.
The role of soldiers in foraging
Due to their physical appearance, it can be easy to assume that soldier termites are primarily focused on colony defence. However, they play a significant role in termite foraging.
Soldiers in Nasutitermes corniger are involved in finding food sources and recent research has shown that the presence of soldiers can impact the tunnelling behaviour in some species of Reticulitermes.2 Trials with live soldiers produced more tunnel branches in R. flavipes, while trials with live soldiers or even the chemical extract of a soldier increased tunnel speed in R. flavipes and accelerated tunnel initiation in R. hageni. However, in R. virginicus, there was little impact of soldiers on the tunnelling behaviour. For termites embarking on foraging into new territories, there is clearly increased risk of encountering competing colonies and predators, so there is an obvious evolutionary benefit in having soldiers present when foraging.
However, as always, in understanding termite behaviour it is important not to assume all species behave in the same way. Apart from the lack of impact of soldiers on the foraging behaviour of R. virginicus in this study, other researchers have also found that the presence or absence of soldiers had no impact on worker exploratory behaviour in Coptotermes formosanus.3
Tunnelling/food transportation efficiency
Observing and measuring termite tunnelling activity and especially food transportation in the field is difficult, for obvious reasons. Three different food transport behaviours have been suggested in social insects: individual transportation of food from the feeding site back to the nest; a ‘bucket brigade’ process by which individuals pass on food part way back to the nest; and an indirect transfer process, whereby termites drop off goods at a staging post, to be pick up by other individuals. Investigating the first two of these possible food transport behaviours, researchers have developed an individual-based model to simulate the food transport process, to understand what types of behaviours are likely to lead to the most efficient process.4
They explored the effect of four variables on the efficiency of food transport: the frequency of food transfer, the loss of food during transfer, the effect of tunnel curvature and the number of individuals participating in the food transport. The model demonstrated that the frequency of food transfer had the biggest impact on food transfer efficiency. Furthermore, it suggested that when the distance between the food and nest was short, that there should be no food transfer (termites would take food directly back to the nest), but for long and narrow tunnels (with a high chance of traffic jams), food transfer becomes a more efficient way to get food back to the nest.
Transporting food in a straight line between a food source and the nest would generally be the most efficient route, saving time and energy. But for termites, who generally explore for food in a somewhat random manner, creating many branched tunnels, it was unknown whether termites would modify their foraging tunnels after finding a food source to improve efficiency.
Researchers at the University of Florida investigated the tunnelling behaviour of Coptotermes formosanus in the laboratory.5 When offered a straight pre-formed tunnel between the nest and feeding site, termites continuously used the tunnel with minimal efforts to create new branches.
However, for termites that were offered preformed tunnels with many twists and turns between the nest and the food site, their behaviour changed. They only used the pre-formed tunnels for a few hours before starting to initiate a large number of alternative branches.
This tunnelling behaviour ultimately created shorter commuting distances between the nest and the feeding site, and these tunnels were widened over time. The conclusion was that C. formosanus could indeed modify its foraging tunnels by making them shorter and wider to increase foraging efficiency.
How does food availability effect termite survival and reproduction?
Colonies of social insects are dynamic with their demography (composition) changing over time. They can also be impacted by disease and resource availability (food and water). Researchers have recently studied the impact of restricting food on a primitive drywood termite, Cryptotermes secundus.6
With a low level of social complexity and living in small colonies with around 100 workers, it allowed for whole-of-colony assessments in the laboratory. Interestingly they found that restricting the food did not impact the survival rates of individual queens and workers, or indeed the whole colony. However, it did reduce the egg-laying capacity of the queen. It also stimulated the development of more alates (workers in Cryptotermes can develop into alates). This behaviour makes sense from an individual and colony point of view – workers developing into alates can move to a different location where (hopefully) there is more food. This reduces the food demand of the colony thus increasing its chances of survival, but potentially allows the colony to continue should the original colony die out.
References
1 Gazal, Vinicius & Bailez, Omar & Viana-Bailez, Ana. (2023). Salivary gland substances of the arboreal termite Nasutitermes corniger induce worker aggregation and gnawing of food substrate. Entomologia Experimentalis et Applicata. 171. 10.1111/eea.13291.
2 Janowiecki, Mark & Vargo, E.. (2022). Effect of soldiers on collective tunneling behavior in three species of Reticulitermes (Blattodea: Rhinotermitidae). Insectes Sociaux. 69. 1-9. 10.1007/s00040-022-00864-6.
3 McCarthy, Joseph & Khadka, Arjun & Hakanoğlu, Haşim & Sun, Qian. (2023). Influence of Soldiers on Exploratory Foraging Behavior in the Formosan Subterranean Termite, Coptotermes formosanus (Blattodea: Rhinotermitidae). Insects. 14. 198. 10.3390/insects14020198.
4 Lee, Sang-Hee & Park, Cheol-Min & Lee, Sang-Bin. (2022). Exploring the efficiency of termite food transportation in a sinusoidal-shaped tunnel. Ecological Modelling. 474. 110180. 10.1016/j.ecolmodel.2022.110180.
5 Michael, Zion & Chouvenc, Thomas & Su, Nan-Yao & Lee, Sang-Bin. (2023). Finding shortcuts through collective tunnel excavations in a subterranean termite. Behavioral Ecology. 34. 10.1093/beheco/arad007.
6 Lin, Silu & Pen, Ido & Korb, Judith. (2023). Effect of food restriction on survival and reproduction of a termite. Journal of Evolutionary Biology. 36. 10.1111/jeb.14154.
Termite Professional Australian edition, 2022
Where do termites get their nitrogen from?
Nitrogen is essential for growth — a building block for proteins. However, most termite food is protein poor and therefore nitrogen deficient. So how do termites get their nitrogen?
It is known that diazotrophic bacteria are present in termite guts and nitrogen fixation by these bacteria has been considered an important pathway for nitrogen acquisition by termites. Certainly, this is proven for species that may spend all their life within one piece of wood such as the Kalotermitidae. However, recent research on Coptotermes formosanus suggests that this may not be the case for all termites, especially those with easy access to soil.1
Young Coptotermes colonies raised on nitrogen-rich organic soil developed significantly faster than colonies raised on inorganic sand. In addition, the development of colonies raised on organic soil stopped when access to organic soil was removed. It appears that the termites were directly consuming the soil, which provided a readily available source of nitrogen. The other potential source of nitrogen is through eating dead nestmates or exuviae (old cuticles from moulted termites). However, although it is known that cockroach exuviae contain high levels of nitrogen, it was unknown if it was the same case for termite skins.
Analysis has revealed that the nitrogen level of the exuviae of Coptotermes gestroi workers was higher than in whole worker bodies and significantly higher than in wood or organic soil.2 The researchers concluded that the consumption of exuviae after the moulting process plays an important role in nitrogen conservation in termites.
Just add salt
Given the poor nutritional status of wood, it makes sense that termites should seek out additional sources of nutrients and minerals. Obviously, the soil itself can be a source of nutrients, but soils themselves vary greatly in nutrients. Recent trials in nutrient-poor savanna soils illustrated this point. In such an environment, salt is needed by animals, but is in short supply within the environment. Researchers therefore hypothesised that termites were sodium-limited in their diet and would therefore seek out potential sources of sodium.3 Treating plots with varying amounts of either sugar or salt solutions, the researchers confirmed the hypothesis with termites proving 16 times more likely to occur in plots supplemented with 1% sodium chloride (salt).
Termite behaviour at the feeding site
Although much research has focused on the tunnelling behaviour of termites searching for food, there is little knowledge of foraging behaviour once a food source has been located. Recent research has started to unravel these behaviours. Working with two-year-old Coptotermes formosanus worker termites in the laboratory, researchers established that workers spend significantly more time at a foraging site than at a non-foraging site and they identified two groups of workers.4
One group, on immediately entering the food site, started chewing up food fragments, passing the resulting bolus onto the second group, the recipient workers. These workers then took the food back towards the nest. However, given that some of these workers often quickly returned to the feeding site, empty mouthed, it was assumed the food bolus was passed to other termites in the tunnel, as part of a passing chain back to the colony.
References
1 Mullins, Aaron & Chouvenc, Thomas & Su, Nan-Yao. (2021). Soil organic matter is essential for colony growth in subterranean termites. Scientific Reports. 11. 10.1038/s41598-021-00674-z.
2 Tong, Reina & Aguilera, Daniel & Chouvenc, Thomas & Su, Nan- Yao. (2021). Nitrogen content of the exuviae of Coptotermes gestroi (Wasmann) (Blattodea: Rhinotermitidae). Heliyon. 7. e06697. 10.1016/ j.heliyon.2021.e06697.
3 Clay, Natalie & Shepard, Donald & Garda, Adrian & Mesquita, Daniel & Vasconcellos, Alexandre. (2022). Evidence of sodium limitation in ants and termites in a Neotropical savanna. Journal of Tropical Ecology. 38. 1-8. 10.1017/S0266467421000535.
4 Lee, Sang-Bin & Chouvenc, Thomas & Su, Nan-Yao. (2021). Differential time allocation of foraging workers in the subterranean termite. Frontiers in Zoology. 18. 10.1186/s12983-021-00446-5.
Termite Professional Australian edition, 2021
The impact of environmental factors on foraging behaviour
In a termite inspection report, the pest manager will record the potential risk level of a termite attack as low, moderate, high or very high. But what are the key factors that increase the risk of termite attack?
Using in-ground monitoring stations, researchers in Indonesia1 mapped termite activity across a city and determined that soil characteristics and climate(temperature and humidity) impacted the incidence of termite attack, but didn’t affect the intensity or frequency of termite attack. In particular, with reference to soil characteristics, it appeared that increased levels of clay in the soil was correlated with increased termite activity (clay packing illustrated above), probably due to its higher nutrient content and optimal texture for tunnelling and nest building.
In a more in-depth study on Coptotermes formosanus, researchers2 found that termites preferred monitoring stations containing clay, rather than stations filled with other soil types or those left unfilled (wood only). Monitoring stations containing clay were not only preferred, but under low moisture conditions increased the survivorship of termites (they had a high body water percentage) and resulted in increased wood consumption. Interestingly, different clay soils were preferred at low and moderate moisture levels – bentonite was preferred at low moisture levels and chlorite or attapulgite preferred at moderate moisture levels. The researchers concluded that the preference for bentonite at low moisture levels was due to its ability to retain moisture whereas the preference for chlorite and attapulgite at moderate moisture levels (where the risk of desiccation was minimal) was possibly based on the increased ability to acquire micronutrients from these soils.
Although having an understanding of the general foraging behaviours of termites is important, when considering how termites are likely to behave in a particular situation, it is important to take into account local conditions. Researchers mapping termite activity in eucalyptus plantations in Africa,3 using in-ground monitoring stations, found that temperature was positively correlated with the number of baits attacked and amount eaten, as expected. But they also found that termite activity actually increased through the dry season, which on the face of it may seem counterintuitive, as termites have a need for moisture and high humidity. However, in this particular environment, alternative food sources became scarce during the dry season leaving the eucalyptus plantation and the monitoring stations as the only significant food source. In addition, although subterranean termites do require an environment with high humidity, overly wet or waterlogged soil makes movement difficult in the wet season and lowers the soil temperature, potentially reducing termite activity.
It is important to appreciate that conditions outside a building in the soil are very different to the conditions inside a building. For example, even in cooler months termite activity inside a building may continue, especially in buildings with heating. However, the external conditions are certainly important when assessing the risk of attack and identifying potential entry points. External conditions can also influence the placement of in-ground monitoring or bait stations, to maximise station discovery and termite attack.
Do termites focus on larger food sources?
It makes sense for termites to recruit to the largest food source in their territory. Obviously in many cases this is a building. Termites tend to forage in areas where the surface soil contains more moisture, which tends to be under large objects such as fallen trees, but can termites really determine whether one food source is bigger than another?
Recent laboratory research with Nasutitermes corniger assessing termite reaction to food sources (by varying the number of wooden blocks offered), suggests that the initial exploration and initial recruiting behaviours are not influenced by the size of the food source. However, mass recruitment was significantly higher to the larger wood sources, suggesting that termites are capable of discriminating between food sources and selecting the larger resource.4
The role of soldiers in foraging
The soldier caste, as the name suggests, is integral to the defence of termite colonies. However, recent research also indicates that soldiers have a role in foraging too.5
Carrying out a series of laboratory trials using Nasutitermes corniger, researchers compared the foraging performance of groups comprising 30% soldiers (the natural ratio found in the field) to the performance of groups containing no soldiers. Groups with soldiers occupied a larger number of food sources more quickly than groups without soldiers. In addition, when the size of food resources was manipulated, groups containing soldiers were faster to switch their foraging effort to the larger food resources.
The researchers concluded that the presence of soldiers in foraging groups promotes faster decision-making during foraging. On the face of it, having a foraging force comprising 30% soldiers – termites unable to actually collect food due to their nasute heads – would make foraging less efficient. So from an evolutionary point of view, the efficiencies gained through the increased speed in decision-making and the exploitation of larger resources due to the presence of soldiers must offset the drop in efficiency by having fewer workers in the foraging party.
Termites are always looking for new food sources
It’s not uncommon to observe different termite species utilising the same resources and even the same tunnels. But is this just by accident or could there be some other factors at play? Working with Nasutitermes corniger, a group of researchers in Brazil investigated whether odour cues left by different colonies of the same species or from colonies of different species impacted food choice.6
The studies showed that the termites could detect chemical cues left by different N. corniger colonies but they seemed unable to detect chemical cues of Coptotermes gestroi, which was used as the different species in this trial. Although workers followed trails with their own chemical cues for a longer distance than trails made using chemical cues from other colonies, when the odours from other colonies were added to a food source, the termites preferred these food sources to food sources containing their own chemical cue. Indeed even food lacking in any termite chemical cues were preferred to food with their own colony odour. This would suggest that termites actively discover and evaluate new food sources over previously detected food sources and that chemical cues from other colonies may aid in this decision.
Assuming this behaviour is replicated across termite species, it suggests that fresh termite baits lacking in colony chemical cues placed at foraging sites will be actively explored. Acceptance however, will depend on bait palatability.
References
1 Arif, A., Putri, G., Muin, M., 2020. Hazard Mapping of Subterranean Termite Attacks in Makassar City, South Sulawesi, Indonesia. INSECTS 11. https://doi.org/10.3390/insects11010031
2 Jin, Z., Chen, J., Wen, X., Wang, C., 2020. Effects of clay materials and moisture levels on habitat preference and survivorship of Formosan subterranean termite, Coptotermes formosanus Shiraki (Blattodea: Rhinotermitidae). PEERJ 8. https://doi.org/10.7717/peerj.10243
3 Alamu, O.T., Ewete, F.K., n.d. Influence of seasonal changes, weather factors and soil depth on the foraging activities of subterranean termites in Eucalyptus plantations. INTERNATIONAL JOURNAL OF TROPICAL INSECT SCIENCE. https://doi.org/10.1007/s42690-020-00311-8
4 de Souza, T.S., Gazal, V.S., Aguiar-Menezes, E. de L., Fernandes, V.J., Leite-Mayerhofer, A.M., 2020. INFLUENCE OF THE AMOUNT OF FOOD RESOURCES IN THE FORAGING BEHAVIOR OF Nasutitermes corniger (MOTSCHULSKY). BIOSCIENCE JOURNAL 36, 48–56
5 Marques do Sacramento, J.J., Cristaldo, P.F., Santana, D.L., Cruz, J.S., dos Santos Oliveira, B.V., dos Santos, A.T., Albano Araujo, A.P., 2020. Soldiers of the termite Nasutitermes corniger (Termitidae: Nasutitermitinae) increase the ability to exploit food resources. BEHAVIOURAL PROCESSES 181. https://doi.org/10.1016/j. beproc.2020.104272
6 Silva, A.N.F., Silva, C.R., Santos, R.E.C., Arce, C.C.M., Araujo, A.P.A., Cristaldo, P.F., 2021. Resource selection in nasute termites: The role of social information. ETHOLOGY 127, 278–285. https://doi.org/10.1111/ eth.13125
Further reading:
General information on termites
Termite predator avoidance:
How termites use sound to avoid predators?
Termites can hear ants coming!
How do termite hear predators?
Termite food choice:
How do termites decide which food source to exploit?
Termite cannibalism in starving colonies
Termites damage to plastic cables
Termite tunneling:
Division of labour during termite tunneling
Termites as structural engineers – How they stop homes collapsing as they feed.
