Insect antennae are the most wonderful sense organs. They are both the nostrils and feelers – tactile probes – of insects, and are covered with an array of sensory receptors that can be used to detect a host of different things, including: potential mates, hosts, prey items, oviposition sites and much more. They are used in so many ways and are so useful, it’s a wonder we all don’t have them!
Insect antennae come in many shapes and sizes, and virtually all insects possess them. In many species, especially moths, they have evolved to become highly efficient, extremely sensitive devices for detecting airborne chemicals: pheromones. The antennae of the male silkmoth, Bombyx mori (below), is almost as sensitive as the nose of a dog, being able to detect single molecules of the female sex pheromone.
As well as odours, antennae can also detect touch, gravity, wind, and sound. One of the best-studied of all antennae, is that of the fruit fly, Drosophila melanogaster. Olfactory receptors located on hair-like sensilla on the antennal lobes detect odours and pheromones, and antennal ears , yes ears, detect acoustic signals, such as the male courtship songs, as I described in another blog: A courtship duet.
Insect antennae come in all shapes and sizes (below), from the tiny little dragonfly antennae, to the very large antennae – sometimes much longer than the body – of longhorn beetles. There is huge diversity of insect antenna, which I will touch on in this blog. To describe them all would require a book!
I was able to creep on this male Emperor Dragonfly (Anax imperator)and get a close up image (heavily cropped) of the head, which shows the tiny antennae marked with arrows (below).
Longhorn beetles (Cerambycidae) have extraordinary antennae which are covered in many different types of sensillae that enable the beetle to taste, smell and feel its environment. It addition, there are also chemo-, thermo- and mechanoreceptors which make it an all round chemical, physical and motion sensor device! Twelve different types of sensilla were discovered on the antennae of the red-necked longhorned beetle, Aromia bungii. (Di Palma et al., 2019).
Another example of an insect with really tiny antennae, is this little planthopper from Thailand (below). What it does with tiny, hair-like sensors, I have no idea.
I have long pondered the function of antennal brushes, like those on this longhorn beetle from South America, Batus barbicornis (below).
I have not been able to find a good research paper on tuft-bearing longhorn beetles. The antennal structures are used by taxonomists to classify these beetles, but exactly how the beetles use these tufts – I don’t think it is for cleaning out little chimneys! – is a bit of a mystery. Cerambycids are incredibly good at detecting long-range attractant pheromones, and the structures seem to be present on both sexes. They might be sexual ornaments, as well as having useful functions.
The lovely beetle, Diastocera wallici tonkinensis (below), named after Alfred Russel Wallace I think, appears in large(ish) numbers at a certain time of year (end of March) in Thailand. Bearing its antennal tufts!
There are many insect, beetles included, which have close associations with ants. Large and elaborate antennae often develop in such myrmecophilous species, like the one shown below, from Laos.
Little is known also, about the exotic beetle shown below, Colilodion schulzi sp. n. from Palawan, the Philippines, which was described from a single female specimen (Yin et al., 2020). What does it do with the three-segmented antennae with conspicuously broadened apical antennomeres, I wonder?
As I mentioned, these huge elaborate antennae often develop in species, living in the nests of ants, perhaps to provide the ants with glandular secretions. A sort of mobile food dispensary? In these ant nest beetles, in the subfamily Paussinae (above and below), these antennae are sometimes said to be used as handles by ants to drag the beetle around the nest! I think it is more likely that the ants were feeding on secretions from the antennae, and the beetle was moving, so it looked like the ants were pulling it about?!
That’s enough for one blog. I’ll write some more about different kinds on insect antennae in another contribution!😊
Di Palma, A., Pistillo, M., Griffo, R., Garonna, A. P., & Germinara, G. S. (2019). Scanning electron microscopy of the antennal sensilla and their secretion analysis in adults of Aromia bungii (Faldermann, 1835)(Coleoptera, Cerambycidae). Insects, 10(4), 88.
Yin, Z. W., & Cuccodoro, G. (2020). Colilodion schulzi sp. n.(Coleoptera: Staphylinidae: Pselaphinae) from Palawan, the Philippines, with habitus photographs and a revised key to all Colilodion species. Revue suisse de Zoologie, 123(1), 153-158.