Most of the time, an unusual invasion of six-legged creatures in the suburbs will make a homeowner freak out. Not this time.
The suburbs are awash in a sea of pretty Red Admiral butterflies.
"We've been flooded with questions about that," says butterfly expert Doug Taron, curator of biology at Chicago's Peggy Notebaert Nature Museum and a steward for the Bluff Spring Fen in Elgin. "It's a common species, but not usually this common."
He is used to seeing fluctuations in butterfly numbers, especially among Red Admirals with their black, white and red wings.
"This is a species known to periodically experience big population booms followed by big population busts," Taron says. But this current population boom surprises even Taron during his recent outing at the Bluff Spring Fen.
"The real story continues to be the admirals," Taron writes in his butterfly blog. "I don't know how long it will last, but I've never seen this species undergo such a huge population explosion."
Even on a cool day, the butterflies make him take notice.
"Generally, you don't see butterflies terribly active under 65 degrees, and it was in the low 50s," notes Taron. "There were just dozens and dozens of butterflies chasing each other around the nettles."
The butterflies feed on the stinging nettle plants at the fen, but even with their increased numbers, the Red Admirals don't threaten any plant life.
"I would say they are up at least tenfold above their normal abundance," Taron says, adding that the population boom also seems to cover a wider area of the Midwest and that the butterflies started showing up earlier than in normal years.
While it might be tempting for people to attribute the increase to global warming, it's not that simple, Taron says. Nature is complicated. In addition to the Red Admiral increase, Taron says he also saw some tiny blue Spring Azure butterflies in March, more than a month ahead of schedule. The mild winter and the record warmth in March might have something to do with the high point in butterfly population.
"Or it may be as simple as their parasite load may be at a low point in its cycle," Taron says, explaining how a drop in the number of tachinid flies and wasps that dine on caterpillars could translate into more butterflies.
As common as they are, the Red Admirals are still pretty interesting to Taron, who also is director of the Illinois Butterfly Monitoring Network.
"They don't overwinter here," Taron says, explaining how the insects flutter up here every spring from the Gulf Coast. "If they migrated in these numbers every year, you'd probably hear more about them."
The monarch butterflies draw plenty of tourists and media attention with their spectacular round-trip migrations in the spring and fall. Not as many Red Admirals make the trip each spring, and it's just a one-way trip. The adults die when it gets cold, and the process begins anew in the spring when the eggs hatch in the South.
The Red Admirals generally come up here and enjoy two or three generations before they die off. "They got started so early, it would not surprise me if they sneak in an extra generation this year," Taron says. A warmer-than-average fall might also sustain the population boom longer than expected.
"Nature is so complicated that beyond a couple of steps out, it's very difficult to predict what's going to happen," says Taron. Noting that predators always get a say in nature, Taron is willing to make one prediction, given all the fat, juicy, tempting Red Admiral caterpillars that are popping up this spring.
"I think," Taron concludes, "that the warblers will have a very nice spring."