by Matthew Cobb
This video is not for the wasp-phobic. What looks like a flower is in fact a wasps’ nest, from Central America. The wasps are clustering over their brood – the future of the colony.
The species concerned is Apoica pallens – I guess the “pallens” refers to the weirdly pale abdomens. The reason why they are so pale – and so relatively calm – appears to be that they are nocturnal (there are two genera of nocturnal wasps, Apoica and Provespa). Here are two photos from here, and here
A. pallens also shows visual adaptations to a low-light environment. In 2006 Birgit Greiner pblished an article on the A. pallens visual system (isn’t science brilliant? Someone has devoted months, or longer, to studying the visual neuroanatomy of a nocturnal wasp from Panama. In fact, this was Greiner’s PhD research, which she carried out in the lab of Ian Meinertzhagen in Dalhousie, Canada, a world expert in insect visual anatomy.)
Greiner has a neat description of the ecology of this species:
The nocturnal polistine wasp Apoica pallens belongs to the social wasps in the New World tropics (Jeanne,1991). It shows a novel method of swarm founding, where a distinct calling display initiates explosive emigrations (Hunt et al.,1995; Howard et al.,2002). These swarm emigrations mostly take place during dusk and Howard et al. (2002) therefore suggest that falling light levels may act as the initial stimulus to move. Even though the nocturnal wasps guard the nest and cool the colony by fanning their wings during the day, visual foraging activities, including flower visits and collection of arthropod provision for their larvae, only occur at night (Vesey-FitzGerald,1938; Schremmer,1972; Hunt et al.,1995). In a complicated tangled rainforest this requires sophisticated navigation abilities and a sensitive visual system. As in nocturnal bees, Apoica‘s large eyes and huge ocelli further indicate that specific adaptations to dim-light vision are likely to be present (Kerfoot,1967a; Schremmer,1972; Engel,2000; Thi Phuong Lien and Carpenter,2002).
Here’s Greiner’s figure 1: A. pallens is on the left, and the diurnal (day-flying) Pollistes occidentalis is on the right. NB both these samples are females – males play a pretty insignificant role in social hymenoptera (bees, wasps and ants) being basically just flying sperm.
The antennae have been broken off (the stumps are the paired round structures in the centre of both heads), presumably to produce a clear image of the eyes. You can see that the compound eyes are proportionately much larger in A. pallens than in P. occidentalis, and also that the three ‘ocelli’ (‘little eyes’) are much more prominent. In diurnal insects the ocelli detect polarised light and movement – whatever they are doing in A. pallens, they are clearly massive. Greiner confirmed these impressions by counting and measuring the number of facets on the compound eyes: more facets (9000 vs 7000 roughly), larger eyes despite the head being smaller (10% larger eye area); when you take the different head size into account, “the nocturnal wasp has a 1.8 times larger relative eye size than the diurnal species”.
A. pallens also has hairs on its eyes (not quite so gruesome as it sounds) and above all has a different internal anatomy in its facets, producing a 25-fold higher sensitivity in the nocturnal species, primarily due to the photoreceptors being wider in A. pallens. Strikingly, Greiner suggests this difference is not enough to account for their ability to ‘see in the dark’ – there must be some kind of processing in the brain that enables these insects to manoeuvre in low light levels.
In 1995, Hunt et al wrote:
Nests are sited on small diameter, near-horizontal branches in a variety of shrub and tree species. During the day, adult wasps cluster on the face of the nest in an array that seems to be determined by orientation to gravity; defense of the colony against parasitoids and ants by the resting wasps may be more a passive than an active behavior. Wasps fan their wings to cool the colony during the day, but no foraging for water accompanies the fanning behavior. Nightly foraging activity begins with the explosive departure from the nest of hundreds of wasps, most of which rapidly return. Moderate foraging levels early at night give way to very low foraging levels in pre-dawn hours. The period of moderate foraging may be extended for longer hours during increased moonlight. Foraging wasps collect arthropod provisions for larvae. Larvae produce a trophallactic saliva; adults engage in inter-adult trophallaxis; brood are cannibalized. During cluster formation prior to swarm emigration, adult wasps do not appear to scent-mark substrates such as leaves. (…) Swarms can emigrate during the day.
So they don’t really ‘see in the dark’. In a 2005 paper , Fabio Nascimento and Ivelize Tannure-Nascimento published this photo of the alarmingly ‘explosive’ departure of the closely related wasp A. flavissima from the nest at dusk:
And the movement of both A. pallens and A. flavissima seems to be related to the phases of the moon. They don’t fly in the dark – they fly by moonlight. That doesn’t sound so intimidating does it?
h/t @bug_girl on Twitter
Fabio S. Nascimento; Ivelize C. Tannure-Nascimento (2005) Foraging patterns in a nocturnal swarm-founding wasp, Apoica flavissima van der Vecht (Hymenoptera: Vespidae. Neotropical Entomology 34:177-181.