Fireflies are one of the coolest insects out there. It is fun to watch them glow at night, emitting a beautiful yellowish green light that they use to attract at mate. One of the biggest threats to a firefly, like with almost any flying insect, is accidently flying into a spiderweb.

Unfortunately (for the fireflies), it seems that the spiders have learned to take advantage of the glow from these insects to bring in even more food.

A study that was published in the Journal of Animal Ecology found that when a firefly gets trapped in a web, it continues to glow for up to an hour. The researchers aren’t sure if this continued glowing is a stress response to their capture or if it is being forced by the venom of the spider. Either way, the results are the same. The glow attracts other fireflies to the web, which means more food for the spider.

This study was done on the sheetweb spider (Psechrus calavis), which builds a web between trees or rocks. These webs are usually around 10-70 centimeters (4-27.5 inches) off the ground, which is a great height for these fireflies since the females typically don’t fly like the males.

Researchers from Taiwan placed the male fireflies onto the spider web and then watched to see what they did for 90 minutes. Interestingly, their glow, which was kept study in one location since they were trapped, resembled the glow of a female. The males flying in the area would make the deadly mistake and fly down to what they thought was a female looking for a mate, only to get entangled in the web.

The researchers also simulated the firefly glow using LED lights and got similar results, showing that the insects are drawn down to the area where they become prey for the spider. Dr I-Min Tso is the lead author of the study, and in a statement said:

“This study sheds new light on the ways that nocturnal sit-and-wait predators can rise to the challenges of attracting prey.”

It was thought that this may not be an intentional action from the spider, if they just happened to ignore the firefly for a time before consuming it for reasons beyond trying to bring in more prey. The researchers, however, found that when another insect, such as a moth, got trapped in the web, the spider would immediately go over to eat. For the firefly, however, the spider saved its dinner for later, making sure that it could not escape while its glow attracted more guests to the party. Dr Tso commented on this, saying:

“Handling prey in different ways suggests that the spider can use some kind of cue to distinguish between the prey species they capture and determine an appropriate response. We speculate that it is probably the bioluminescent signals of the fireflies that are used to identify fireflies enabling spiders to adjust their prey handling behavior accordingly.”

This reveals a level of understanding that these spiders have developed, which is beyond what many would have expected. These spiders use a surprisingly complex hunting technique that has proven to be very successful.

If you thought that was interesting, you might like to read about why we should be worried about the leak in the bottom of the ocean.