Insect antennae often play important roles in courtship and mating. Not just for detecting pheromones, as we saw in the last blog, but also for transferring them, and for stimulating the opposite sex. Antennation – using the antennae to touch any part of the body of another insect – occurs for a variety of reasons and allows insects to exchange physical and chemical information with each other. As wrote in a blog about the Insect Cuticle, insect’s bodies are covered in waxes – cuticular hydrocarbons – primarily to reduce water loss, but they also convey a wealth of information about the age, sex, and health of the insect.
An insect can, in theory, read this ‘chemical book’ by touching the body of another with its antennae. But why their antennae have specific patterns, shapes and colours (like the little wasp, shown above), is much harder to elucidate, and could be for a number of reasons, perhaps to do with mate or species recognition.
Hymenoptera, wasps in particular – like the fabulous Asian giant hornet (Vespa mandarinia) (above) – are a group where the antennae often play an important role during courtship and mating, with the male drumming, stroking or grabbing the female’s body or antennae! Here (below) is another invasive hornet, the Asian hornet (Vespa velutina), which I photographed in Spain. The males’ antennae are longer than those of the female, but you would need the two side by side to compare them. The antennae are large and robust and no doubt highly sensitive to a range of chemicals and pheromones. This wasp raises up its antennae and front legs and shakes its wings when it feels threatened. That’s the time to run! Incidentally, the so-called ‘murder hornet’, Vespa mandarinia (above) hunts the Asian hornet, V. velutina (below)! (Kwon and Choi, 2020).
In some blister beetles (Coleoptera, Meloidae), especially in in the subgenus Meloe (below), courtship involves a form of antennal grasping. In these species, the males grasp the female’s antennae with their own antennae and repeatedly pull them in and out of grooved depressions on their heads (Pinto, 1975). In other species, there are specially adapted segments on the male’s antennae which are modified for grasping (see below) (Pinto and Selander, 1970).
The female’s antennae are held, by the male bending his antenna at an articulation point (below). The male is probably doing this to transfer a sex pheromone to special receptors on the female’s antennae. The pheromone will make the female more receptive and copulation can occur if she likes what she sees and tastes!
It’s always worth reminding ourselves that there is usually a tremendous diversity of forms and functions, even within a single insect family, and what is true about antennae in one species, might not be the case in another. Here for example, is a very unusual Mylabris beetle (Meloidae) from Africa (below). How does it use its antennae I wonder? The photographer relates his rather unusual experience when collecting this specimen: “ I had the unfortunate experience of storing a bunch of these in my pocket while in the bush. Later that night my upper thigh was covered in large blisters.”
Antennae are very useful for touching and tasting, and there are lots of different sensillae, many of which are concentrated on the tips. Bees can recognize fine differences in the textures of flower petals using the tips of their antennae (Kevan and Lane, 1985). They can also sense a lot more about the odour and chemistry of the plants they visit.
Honeybee male drones have antennae which are specifically designed for the detection of queen pheromone, and are covered with more than 16,000 sensilla, many of which are sensitive to the queen pheromone; many more than the antennae of a worker bee’s (below) antennae (Robertson and Wanner, 2006).
Apparently, the antennae of bees droop downwards, and stop moving, when they sleep! I only have one picture of a sleeping (or at least resting!) bee (below) and the antennae don’t seem to have dropped, or drooped very much! A bit. Perhaps it was just dozing; worn out by carrying around such large pollen sacs!
Male long horned bees have unusually long antennae, in some species, exceeding the length of the body. The females have much shorter antennae; the antennae of Eucera males have three times more olfactory receptor neurons than the females’ (Streinzer et al., 2013), perhaps to detect sex pheromones produced by the ladies.
So we have seen that antennae have often evolved for courtship and mating purposes, and males often have longer, larger and more sensitive antennae than females. But as always in nature, there will probably be examples where the opposite occurs!
Previous blogs on this subject
Kevan, P. G., & Lane, M. A. (1985). Flower petal microtexture is a tactile cue for bees. Proceedings of the National Academy of Sciences, 82(14), 4750-4752.
Kwon, O., & Choi, M. B. (2020). Interspecific hierarchies from aggressiveness and body size among the invasive alien hornet, Vespa velutina nigrithorax, and five native hornets in South Korea. PloS one, 15(7), e0226934. https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0226934
Pinto, J. D. (1975). Intra-and interspecific courtship behavior in blister beetles of the genus Tegrodera (Meloidae). Annals of the Entomological Society of America, 68(2), 275-285.
Robertson, H. M., & Wanner, K. W. (2006). The chemoreceptor superfamily in the honey bee, Apis mellifera: expansion of the odorant, but not gustatory, receptor family. Genome research, 16(11), 1395-1403.
Streinzer, M., Kelber, C., Pfabigan, S., Kleineidam, C. J., & Spaethe, J. (2013). Sexual dimorphism in the olfactory system of a solitary and a eusocial bee species. Journal of Comparative Neurology, 521(12), 2742-2755.
Wittmann, D., & Blochtein, B. (1995). Why males of leafcutter bees hold the females’ antennae with their front legs during mating. Apidologie, 26(3), 181-196.