Written by Joe Ballenger
You Question! Or Comment. =): Do you have any knowledge on insects in western Canada during/following wildfires? Do certain insects have protective measures they take during wildfire, or do they just leave the area?
Morning Commute pic.twitter.com/yAqZQjYLnp
— Nature is Scary (@NatureisScary) December 13, 2017
For the people living in California, it kind of sucks that this is a relevant question. It sucks that a lot of people have lost their homes, or their lives…and it’s really hard to write a post like this without acknowledging their tragedies.
However, at the same time, there’s an ecological reason for this. Wildfires, in many environments, are a normal part of life. Lots of plants are well adapted to occasionally catching on fire. There’s even an entire field of study for figuring out how and why the environment depends on fire-it’s called fire ecology. Some plants, like Lodgepole pines, need fire to keep existing. Some plants, like Cogon grass and some species of Eucalyptus, have even evolved to purposely catch on fire. There’s even a scientific term for that latter type of plant…they’re called ‘active pyrophytes‘.
The reason large swaths of land occasionally catch fire is pretty easy to understand. Some plants have evolved to snuff out the competition by burning out everything around them. This means that there will be both a layer of fertile soil and no competition for the next generation of plants.
Fire ecology is pretty cool, and we could dedicate an entire blog to how and why various plants use fire to their advantage. But this is a blog about bugs, and each of these plants which have adapted to fires have bugs which eat those plants.
So…how do bugs deal with fires in their natural environment?
Escaping Wildfires: Flying Away and Dying
One of the first things I’m going to point out is that it is a bit weird that I’m lumping flying away from a fire and dying in a fire into the same category. They don’t seem like they’re that similar…but I thought about it while writing this post and they kind of are.
Fires are mostly a somewhat local phenomenon. There are sometimes huge fires, but the majority of fires are pretty small and only take out a relatively small patch of environment before they burn themselves out. While it seems like a big patch to us (and it really is if your house is there), it’s a small part of the overall landscape.
Many insect species have wide ranges. They owe this either to their mobility as adults, or their adaptability to different environmental conditions. Because of this, lots of insects which are currently threatened by fire can pretty easily fly away and find a new home without much of an issue. Those which die during the fire are often survived by members of the same species living outside the burnt area. In both cases, the insects can re-invade once the situation cools off a bit.
Make no mistake: a lot of bugs do die during wildfires. Eggs, galls, immobile stages (like pupae) are cooked under most (but not all) circumstances, and some people take advantage of this to control pests.
However, some insects, like those living at the tops of trees, inside trees, or deep underground do survive.
This is where things get really interesting.
Surviving Fire as a Bug
A lot of bugs have stages of their lifecycles where they’re protected. Grasshoppers, ground beetles, and woodwasps, all lay their eggs in areas which aren’t really harmed by fires.
Woodwasps, like the one in the video above, lay their eggs in rotting logs whose size and moisture content often prevents them from being completely incinerated by everything but the largest fires. They share their habitats with a lot of other critters…worms, millipedes, isopods, cockroaches, all can withstand forest fires if they’re protected by a rotten log.
It’s the same way for other insects, like ground beetles or grasshoppers. Grasshoppers lay their eggs underground, which prevents them from being burnt. Lots of beetles will pupate underground (Colorado Potato Beetles do this, too), and this is also a pretty good protection against fire if you bury yourself deep enough. When you emerge, there will be fresh vegetation, and fewer predators. For the predators which pupate underground, there will be ample prey and fewer hiding spots. It works out well for both types of bugs.
Waiting for the Fire
While some insects simply survive a fire, and make the best of the disaster’s aftermath…others will actively seek out freshly burnt or burning forests.
The reason for this is that after a fire, there’s a large amount of dead and weakened trees. Lots of bugs live in dead trees. For others, it makes sense to prey on trees which aren’t able to fight you off.
The beetle genus Melanophila, as well as a few other insects has infrared sensors in its legs which tell it where the fire is and how to get to it. It will actively seek out burning patches of forest, specifically to lay its eggs in trees which have been injured by fire and which aren’t in a position to fight off the invasion. Melanophila, Syntexis, and Acanthocnemus are notable because they’re frequently seen mating and laying eggs on logs that are still on fire.
To clarify: this doesn’t mean they’re recently burnt. I mean this literally…they’re known to lay their eggs on logs that are still actively burning. Acanthocnemus beetles are even attracted to smoldering ashes. Now, granted…they camp out on the non-burning portions, but it’s still pretty crazy.
Finding a Fire
These insects are interesting to entomologists, because we can use them to develop new technologies for sensing infrared signals. Even though these insects are small, Aradus sp. are less than 1/2 inch (they’re about 1 cm long), they can detect a fire from at least 3 miles (5 km) away.
The way these receptors work doesn’t seem to be in a way similar to how insect eyes work (see Nancy’s post here), but seems to be an entirely new way to detect light. The infrared sensors, pictured at left, aren’t very well understood and scientists aren’t entirely sure how they work in living insects.
The sensors are small fluid filled sacs with a pressure sensitive neuron inside. When infrared light from a fire shines through the pit, small changes in pressure caused by an increase in heat are detected by the neurons.
Presumably, they use other senses, like the smell of smoke, to find the actual fire. It’s likely that the infrared helps them to orient themselves, and point the bug in the direction of the burning forest.
The Bottom Line
Fire is a natural part of the landscape, and plants manipulate it to give themselves a competitive advantage. However, in nature, if there’s something to eat…there’s probably a bug that eats it. This includes plants which set themselves on fire to get rid of the competition.
To deal with fires, they typically avoid them or just reinvade once the fire’s burnt itself out. However, there are quite a few bugs which are highly specialized to seek out fire…which is pretty cool.
- Klocke, D., Schmitz, A., Soltner, H., Bousack, H., & Schmitz, H. (2011). Infrared receptors in pyrophilous (“fire loving”) insects as model for new un-cooled infrared sensors. Beilstein journal of nanotechnology, 2, 186.
- McCullough, D. G., Werner, R. A., & Neumann, D. (1998). Fire and insects in northern and boreal forest ecosystems of North America. Annual review of entomology, 43(1), 107-127.
- Swengel, A. B. (2001). A literature review of insect responses to fire, compared to other conservation managements of open habitat. Biodiversity & Conservation, 10(7), 1141-1169.