On June 22, we turned on the porch light and waited for sundown to see what would be drawn to the light. We didn’t get anything until about 11:00[1], but then I heard something going “Whump! Whump! Whump!” on the window. I thought it was something like a crazed bat at first, it was pretty big. But then, once I netted it, this is what we found:

The smaller moth next to it wasn’t actually that small, it was about an inch across, itself. Here’s a picture that will give a better feel for the size of the big one:

This monster has got to be a Modest Sphinx, Pachysphinx modesta. It certainly isn’t “modest” in size, the name is referring to the fact that the upper wings look like a dark cloak covering the significantly brighter underwings:

One thing you may note looking at the face is that there are no obvious mouthparts. That’s because this is one of those species where the adults don’t eat[2]. They are nothing but mating machines that only live long enough to lay eggs.

The feathery antennae help the males to find the females by scent. There is at least one picture on BugGuide showing these moths mating, and it looks like the females have very large abdomens. This one is slimmer, so I think it’s a male. We were probably going to be biased in favor of catching a male in any case: generally male moths are the ones that do most of the flying. The female moths mostly just sit around releasing scent until one of the males finds her.

There seems to be a trend where moths that don’t feed as adults tend to be large moths. This makes sense: if you don’t eat as an adult, being large with a lot of fat reserves will let you fly for longer than a few hours, which boosts the odds of mating successfully. So, there is a lot of selection pressure for larger size. And, there are advantages to not feeding as an adult: it saves a lot of time. If you don’t have to take time to look for food, you can devote all of your time to reproducing the species. And these moths probably don’t have a lot of time to waste, because I’m sure that the bats absolutely love them. Even if they were able to eat, and even if this made it possible, in principle, to live for several weeks, the average one would probably get eaten in the first few nights it is alive. So, they don’t eat so that they don’t have to waste any time, and they are big enough that the time it takes for them to starve is comparable to the time it would take for something to find and eat them.

These are likely to be reasonably common moths, because the food plants of the caterpillars are aspen, poplar, and willow, which are three of the most common trees in this area. The eggs are laid shortly after the moths fly in mid-June, and then the caterpillars eat and grow until fall. At that point, they bury themselves in the ground and pupate over the winter. Then they emerge over a very short time-span in early summer as moths. It was probably a very lucky coincidence in timing that let us catch this fellow, they probably all emerge, mate, lay eggs, and die over a period of about a week, and we just happened to hit that time window.

————-
[1] Of course, that’s because in mid-June, the sun doesn’t go down around here until about 10:00 and it doesn’t get dark until about 11:00. No, we aren’t far enough north to be in the Land of the Midnight Sun, but we have kind of been victimized by the politics of timekeeping. First off, we are in the wrong time zone. The lower peninsula of Michigan is close to the nominal boundary between the Eastern time zone and the Central time zone (and actually more in the theoretical Central time zone). The state evidently was given a choice as to which way to go. For some reason, most of the people with political power downstate decided that it would be advantageous to be in the Eastern time zone, probably because then they’d be synched with Washington DC and New York. The problem is, the western Upper Peninsula is quite a bit west of the Lower Peninsula. The longitude of Houghton is about 88.56 degrees, while the reference longitude for the Central Time Zone (which is supposed to be in the middle of the time zone) is at 90 degrees, so we are waaaaay over in what should be Central Time territory. So, we are already getting sunset darned near an hour later than we really should be. Then, there is Daylight Saving Time in the summer adding another hour on top of that, so the sun is going down two hours late. In a sane world, it would get dark in Houghton in the summer not much later than 8:30 or so, but that is not to be. This kind of bugs me, because if I want to do anything in the summer that requires darkness (stargazing, or collecting fireflies, or watching fireworks), it ends up involving staying up until around midnight[3]. And most of the time, I have to get up and go to work the next day.

[2] There are only some species of sphinx moths that have adults that don’t feed. Many (perhaps even most) species of sphinx moth have very long tongues to drink nectar, and behave very much like hummingbirds, flitting from flower to flower while beating their wings so fast that they are a blur. In fact, they look so much like hummingbirds (and are even the same size) that they are often mistaken for each other. One of our bird books even includes a picture of a sphinx moth in the “hummingbirds” section.

[3] The flip side of our time-zone problem is that in the winter, I go to work before the sun rises, and come home just slightly after it sets, so except on the weekends I might never see natural sunlight at all.