Insects have some tricks to prevent getting too hot or too cold, but, like a sweater in a blizzard, they only work up to a point. These tricks contribute to what scientists call the thermal tolerance of an insect species.
Look closely at any urban or forest tree and you will find hundreds of insect and mite species scattered here and there feeding on leaves or sap. Most never become pests. A few species become pests only after some change in the environment – like warming temperatures. These are called sleeper species.
Outside of cities, in natural environments, it has long been noted that herbivore abundance and feeding increases near the equator where the climate is warmer. But does this latitudinal-herbivory pattern observed in natural areas apply to cities?
We are not the only scientists using cities as surrogates for climate change. However, this line of research is in its infancy. We conducted a literature review, led by postdoc Nora Lahr, to compile all the research we could find in which cities were used to predict the effects of climate change.
Cities are hot and often dry. This makes the plants dry and unhealthy. But what about the animals? They can gain water by ‘drinking’ from moist soil or dew, or by eating plants that are mostly water. But what if they can’t find enough to drink?
A mystery began to nag at me. Some trees in the hottest areas within cities were covered in insect pests and still looked vigorous, while other trees with the same pest densities withered.
Urban yards can be tough for bees. There are often not enough flowers, or the wrong kinds of flowers, so people compensate with pollinator gardens. However, cities are also hot, due to impervious surfaces and the urban heat island effect.
Unless you want an itchy rash, your best bet is to steer clear of these little critters altogether. And if you’re a couple of scientists trying to insert a data logger into a nest filled with two hundred of them? Well, your best bet is to suit up.
For many years, scientists have used forest maps to focus their predictions about where these itchy caterpillars might spread. But, it’s becoming increasingly clear that the PPM doesn’t actually need forests. It just needs trees, and it’s willing to accept the ones in the front yard, thank you very much.
Insects experience the environment at much smaller scales than people do. Some insects may not move more than a block in their lives. We figured bees that can't tolerate heat won't be found in hot parts of town and did a study to determine if that's true.