A look at what we do – and don’t – know about termite swarms.
Termite swarms are a very visible sign of termite activity. Certainly, the appearance of alates in and around a property can be a big cause of concern to the homeowner, and swarming season always generates a peak in phone calls to termite professionals. So what do we actually know about termite swarms?
Termites swarms are the winged reproductives or alates. They are the only termite caste to have fully developed eyes, with a harder cuticle than the soft bodied workers to protect them from the elements (resulting in their darker colour), and two pairs of equal sized wings.
On landing, they drop their wings and the females release pheromones to attract males. They will then pair off and the male will follow the female as they seek a suitable nesting site – a dark, moist area with a preferable food source. They will then excavate a small chamber and mate. The founding king and queen will remain as a pair for life.
Termite swarms are released on warm, humid nights, with little or no wind. This provides the ideal conditions to both maximise mating success – they are weak flyers – and help the founding of colonies. In Australia, swarming will start in spring and continue into summer. The exact timing will depend on the species and the location, with swarms tending to appear earlier in the warmer parts of the country.
It is generally recognised that swarms are produced by mature termite colonies. However, at what stage colonies produce reproductives and under what conditions is somewhat unknown, certainly for the Australian termite species. As with many termite behaviours, the fact that they live underground makes their study challenging. However, one field study on Nasutitermes corniger in Panama at least provides a record of alate production in one species .1
Using data from 49 nests, excavated shortly before their nuptial flights, researchers documented baseline information on alate production. They recorded that alate nymphs developed through five instars and spent between 5-8 months in the parent colony. Mature colonies produced between 5000 and 25,000 alates, representing around 35% of the colony’s biomass shortly before the nuptial flight. Although there were more males than females, when corrected for weight – females were approximately 1.3 times heavier – the ratio of males to females on a biomass basis was close to 1:1. Interestingly, some mature colonies contained no reproductives during the year of census.
This observation highlights one of the big unknowns – what causes a mature colony to produce or not produce alates? Much of the literature simply states that alates are produced by mature colonies, which is undoubtably the case, but do mature colonies produce alates every year? The observations on Nasutitermes corniger in Panama suggest not. So, what conditions are required for alate production?
Investing resources into the development of reproductives is a significant investment by the colony, which is why it is generally only mature colonies that can produce alates. But even then, it is assumed the colonies can only invest energy into developing alates if there is sufficient food sources and moisture available. Certainly during periods of drought, there is the general observation of reduced swarming events.
Of course, it must be remembered that many of the key pest termite species can also produce secondary reproductives. This gives rise to a range of different colony structures: simple families (pair of monogamous primary reproductives), extended families (colonies headed by multiple secondary reproductive descended from a single monogamous pair) and mixed family colonies (where multiple primary or secondary reproductives occur in the same colony).2
There is some evidence to suggest that in species which demonstrate these flexible colony structures, that the production of alates and the creation of simple family colonies is more common under optimal conditions, and that under sub-optimal conditions, the production of colonies with multiple reproductives is more common, presumably as it maximises the chances of survival.
1 Thorne, B.L (1983). Alate Production and Sex Ratio in Colonies of the Neotropical Termite Nasutitermes corniger (Isoptera; Termitidae). Oecologia: 58, 1, pp. 103-109
2 Vargo, E.L. (2019). Diversity of Termite Breeding Systems. Insects. 2019 Feb; 10(2): 52.