Why are female insects more aggressive and bite more than the male ones, but most male mammals are more aggressive and tend to fight more?
In: Biology
I don’t think your premise is totally accurate, there’s just such a huge spectrum of animals involved and you’re over simplifying it. Aside from mosquitoes, can you suggest an overly aggressive female insect with an innocuous male counterpart? I can tell you that female hyenas are terrifying and I wouldn’t want to cross a mama Grizzly either.
I think the trend you might seeing is this-
Insects don’t raise their young (again a generalization) it’s typically a give birth to thousands of babies and hope for the best situation. Where as mammals tend to raise a small number of offspring for a long(ish) period of time.
In this case, the evolutionary trend would be for insects to reproduce as much as possible, so males are just sperm machines and females and just egg machines. Producing sperm is pretty cheap and easy, producing thousands of eggs is nutritionally intense. So female insects will require a lot of nutrient rich food and female mosquitos, for example, feed on blood because it contains tons of sugar and protein for eggs. Male mosquitos do not feed on blood, they just fly around impregnating as many females as possible.
Mammals on the other hand raise their young, which is often done by the females. That essentially takes the females out of hunting/food gathering role, as they are focusing on raising offspring. So the males are simply “out there” where people will see them while the females might be in burrow or somewhere out of sight.
But this is really broad and should not be taken as a universal insight, each animal is unique.
Female insects are often larger than their male counterparts because they need to hold and support the large number of eggs. They also typically do not have help raising their young (with exceptions of hive insects) so they will aggressively defend themselves.
Female mosquitos are a special case where only the females bite and suck blood because they need the extra energy from blood to develop their eggs.
A female mammals doesn’t produce as many young as most insects and their offspring take much longer to raise. Therefore, the most effective reproductive strategy is for a male to be the biggest and baddest to protect a number of females under him. This requires fighting off any other males.
To propagate a species to the next generation you need most of the females to reproduce – but you don’t need that many males.
500 women and one man can produce 500 babies a year. The inverse can only produce one baby.
This has produced significant sexual dimorphism in a lot of species. Males must compete for mating rights (often at the expense of their own survivability) while females are more survival focused.
In insects this sometimes gets quite extreme – the females are larger and more powerful and the males are tiny and exist for little purpose other than mating.
Mammals have largely gone in the opposite direction – intense competition among males has produced larger and more powerful males that can drive off all challengers and any predators. Humans are a moderate example of this, but it can be quite extreme in some species – a dominant male gorilla is twice the size of an adult female.
The instinct driving any animal is the continuation of its own genetic line, even if that is at the expense of others (since other organisms are just competition for resources). That means, ideally, any organism would desire to mate with as many other organisms of the opposite sex while at the same time preventing them from mating with other organisms, thereby ensuring the continuation of its own genetic line and denying the continuation of other genetic lines.
Basically, both males and females would want to “reserve” the other for their exclusive use, but at the same time, would want to procreate as much as possible.
All other things being equal, this is easier for males than females because once a female becomes pregnant, they are already biologically locked down to the male that impregnated them. Ensuring that the female doesn’t procreate with another male simply involves checking in from time to time.
On the flip side, males don’t get locked down like that, so a female trying to reserve a male would basically involve following him around and killing all of his potential mates or simply killing the male.
With mammals, the first strategy is preserved because our long-term survival strategy is to have few young that we devote a lot of resources into improve individual survival capability. So not only do females take on the burden of actual gestation, but then child rearing and education as well. That leaves the males to take on the role of overall protector of the family unit and territory, leading to stronger more aggressive males.
With insects, the strategy is basically to zerg rush the world. Produce as many offspring as is possible, with no sense of care given to them. Thus the strategy is to kill off the male so they can’t impregnate another female who would just produce thousands of competitors for your own offspring. This leads to stronger and more aggressive females.
This is, of course, speaking only in broad strokes and each animal evolves differently.
I’m not sure that this is true in general, but there are still some factors we can talk about.
For one thing, female insects (and spiders, and other arthropods) are often bigger than males. Insects tend to maximize reproduction by producing a large number of young, and bigger females can make more eggs. This pushes females to be larger.
In mammals on the other hand, reproduction is usually maximized by producing fewer offspring and caring for them more effectively. There’s no pressure on females to grow huge to hold large clutches of eggs (or live babies more likely). On the other hand, male mammals often wind up competing with each other for access to females, and big males tend to win these competitions. That drives males to be bigger (although there are also many mammal species where there’s no size difference)
Aside from sheer size difference, another factor that makes female insects more likely to bite is that there are many insects that consume blood. As I noted before, female insects make a ton of eggs. This requires a lot of nutrients. Blood has a lot of nutrients. So many insect species go for blood. Males in many species (mosquitoes for example) don’t even go for blood at all because they don’t have to make eggs.
The situation is different in mammals. Most adult insects live brief lives and just need enough to mate and lay eggs. But mammals live a long time and have to maintain pretty expensive warm blooded metabolisms. Between the need to often maintain a larger body size, and the high baseline need for calories just to live a full life, there’s not such a huge difference in need of nutrients between male and female mammals, so, eg, female tigers aren’t the only ones that hunt meat.
Another notable difference is eusocial insects. Ants, bees, wasps, specifically. In these species, for several reasons but importantly because of a quirk in genetics, worker females are closely related to the queen’s offspring. These workers help defend the nest and the offspring and are thus more likely to sting and bite. Indeed, since the stinger is a modified egg laying apparatus, they are the only ones that _can_ sting. But all this is more of a quirk of one specific type of common insect, not something that’s generally true of all insects.
Of course, “protecting offspring” is a pretty common reason for mammals to attack as well, and female mammals with offspring under threat can be pretty aggressive too.
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