Why do some insects have really fluffy antennae?
Have you ever noticed that some insects have smooth antennae while some seem to have fluffy antennae? Maybe or maybe not. But I do!
Well, here’s an insect insider fact. Most (maybe all) of the insects you see with fluffy looking antennae are male. As in many other animal species, some insects species have sexual dimorphism, which is a fancy way of saying that males and females look different. This can take many forms such as female velvet ants (pictured below) don’t have wings but males do.
Antennae are sexual dimorphic in many insects. In order to talk about why, we need to cover some other stuff about insects. In addition to, or sometimes instead of, using just vision and hearing to navigate the world, most insects can sense their environment through chemicals. This is call chemoreception. Humans use chemoreception too, mainly through taste and smell. But for insects it’s a much bigger part of how they perceive the world and operate within it. Ants can taste the ground they are walking on through chemoreceptors in their feet. Same with butterflies. Herbivorous insects often track chemicals in the air to find the plants they need to eat. Queen honey bees suppress reproduction by female works by putting out lots of a certain chemical. And so much more!
One important way that insects often use chemicals is to find a mate. These chemicals are called pheromones. Females release pheromones that males can use to track them down. This is where the big antennae come in. It’s easier to pick up the pheromones of a female if your antennae have lots of surface area to collect and perceive molecules. The ‘fluffy’ male antennae are really highly branched, providing lots of surface area to sense incoming pheromones. Just look at the surface area of this male midge’s antennae! (I think the overwintering pupae are starting to transform into adults because we’ve seen a couple of them around the house in the last couple days.)
Midges are flies in the Chironomidae family. Some midges bite, but many are non-biting midges like the one pictured above. Female midges lay their eggs on water. Each egg mass can contain up to 3,000 eggs depending on the species. The eggs sink, and then the larvae hatch and bury into the mud. They feed on organic matter in the water and mud. After about 2 weeks, they emerge from the water as adults. Adult midges do not feed and have only 3-5 days to live once they emerge. So finding a mate quickly is important!
I don’t have any good pictures of male moth antennae, but they are also often fluffy in appearance. BugGuide has a bunch of comparisons to look at though. Here is a link to one of male and female Luna moths. As you can see, the male’s antennae are much more branched!
Studies have shown that males in some moth species will track female pheromones over long distances. Their ability find females this way is essential for the survival of the species. This can be exploited by humans who don’t want certain insects in certain places. For example, researchers have developed methods to control pest moths, like codling moth in apples, by releasing lots of female pheromones from traps. The males follow the scent to the traps and are unable to reproduce.
Lots to think about next time you happen to look at ‘fluffy’ insect antennae!