Adult insects rely on their antennae to detect odours (smells!) which tell them all about what’s happening in their neighbourhood. Whether there is anything to eat nearby; whether there are any members of the opposite sex looking for a partner; who else is about, and so on. They wave their wonderful wands around and pick up on all the chemical cues wafting around them!
Of course some species are better than others and have pushed the art of detection to almost impossible limits. As we saw in the previous blog, moths are past masters at this art of detecting one or two individual molecules. In moths, which are largely nocturnal, it’s the females that generally do the calling or attracting, of a mate, i.e. by releasing species-specific blends of volatile pheromones. In the case of the domestic silkworm moth, Bombyx mori (below), it was the first sex pheromone, bombykol, to be discovered (in 1959). And what a detection apparatus the male has to help in find the female!
Females release their sex pheromones in tiny little doses; just a few molecules wafting on the wind. Maybe they are testing the males? Trying to see which is the best one at finding them when they give out such a minimal cue! The males have invested a lot of physiological resources in creating their wonderful antennae, so by releasing tiny quantities of pheromones, the females may be selecting for the best quality males!
If the poor male moths can’t find the female, she releases a bit more pheromone to make it easy for them! As described here. She’s looking for the best male, not just any old chap!
But moths are not the only insects with fantastic antennae. Beetles are also amazingly good at detecting pheromones and other chemical signals in the air. Species like this male Rhipicera beetle (below) have highly elaborate lamellate antennae which function so efficiently because they have greatly increased the overall surface area of the antenna. This effectively changes the airflow across the antennae, and thus the likelihood of them detecting the target molecules.
Of course not all beetles (or moths) have antennae like these. There is such a huge diversity of insects – there are probably millions of beetles (many unknown to us or undescribed) – that all sorts of different antennal types exist. For example, take this little weevil (below). I was really struck by its amazing antennae which it was waving around, when I came across it during a walk through the forest in Thailand. Here is a better picture.
Quite a lot of weevils have these curious antennae, which almost look like portable speakers! There’s a fantastic photograph of a Cercidocerus species from the Congo, here. I would love to know more about how it uses these antennae; there is so much we just do not know about the natural world. For example, despite making great play of the fabulously complex pectinate and plumose antennae in moths (above), most species have rather boring filamentous antennae, like this little chimney sweep (below).
The highly elaborate antennae of moths, and perhaps other species as well, may have evolved to find those really ‘hard to detect’ (i.e. less volatile) pheromones and chemicals (Elgar et al., 2018).
Next time, I’ll look at antennae from a wider ranger of insects, including wasps, bees, bugs, flies and butterflies.
Some related links
Elgar, M. A., Zhang, D., Wang, Q., Wittwer, B., Pham, H. T., Johnson, T. L., … & Coquilleau, M. (2018). Focus: ecology and evolution: insect antennal morphology: the evolution of diverse solutions to odorant perception. The Yale Journal of Biology and Medicine, 91(4), 457.