Despite the fact that scientists have been observing insects and arachnids for many years, they continue to regularly make amazing discoveries. Moreover, this applies even to long-known species that are constantly “in front of our eyes.” This time, researchers discovered an amazing ability in the crossworts (Araneus ventricosus), which are common in China, Japan and Korea. These spiders appear to use live fireflies as bait to attract prey by making them glow in a certain way.
Spiders use fireflies as live bait. Photo credit: nationalgeographic.com
Contents
- 1 How fireflies communicate with light
- 2 Spiders use fireflies as bait
- 3 How spiders make fireflies change their light signals
- 4 Spiders sometimes create a “scarecrow” out of their prey
How fireflies communicate with light
Fireflies use light signals to communicate with each other. However, their “light communication” is quite primitive and comes down to sexual behavior. This means that females communicate that they are looking for males, and males signal that they need a female. Accordingly, in order for the surrounding fireflies to understand who is “winking their flashlight” at them, that is, a male or a female, they use two different light signals.
For example, females of the South Asian firefly Abscondita terminalis send long, low-frequency light signals to males and have only one lantern (glow organ). Males, on the other hand, use fast, short pulses and have two lanterns for this purpose.
Male and female Abscondita terminalis fireflies use different light signals to identify themselves. Photo source: inaturalist.org
On the one hand, light signals allow fireflies to quickly find a “mate”. But on the other hand, their visibility makes them easy prey for predators. In particular, orb-weaver spiders have been found to use them to their advantage.
Spiders use fireflies as bait
Chinese scientists have noticed that some spider webs are full of fireflies, and exclusively male ones. Females are absent from the spider's “webs” or are extremely rare. Of course, this could be a coincidence, but subsequent observations have shown that the presence of only males in the web is a pattern.
Further observation showed that the fireflies congregated in the “webs” where the spiders were. If an insect flew into a completely empty web, it would remain there alone or, at best, with another equally unlucky firefly. This contradicts the hypothesis that, having got into the web, the insect sends a distress signal. Otherwise, there would be even fewer fireflies in the web with the spider.
Spider doesn't kill glowing fireflies, but makes them change their light signal to attract other males. Photo credit: sciencealert.com
How spiders make fireflies change their light signals
The authors of the study decided to conduct an experiment in the field to find out the reason for this oddity – they placed ordinary male fireflies and the same males, but with “flashlights” painted black, in the spiders’ web.
When an ordinary firefly appeared in the web, the spider approached it and made repeated attacks, consisting of a bite and wrapping the prey in web. Moreover, the attacks were made only when the firefly was blinking. As a result of such actions, the males of Abscondita terminalis changed the nature of the signal and began to send impulses similar to those of females. That is, the males infected with the spider’s poison began to attract other males with their impulses, not females.
The spider did the same with the next males that got into the web, and also left them alive, as the authors report in the publication Current Biology. When fireflies with a painted “flashlight” were placed in the web, the spider did not make repeated attacks, but simply ate them.
It remains a mystery to researchers what exactly is causing the change in light signals — the spider's venom or the bite itself. Presumably, the venom somehow switches off one of the lanterns. For example, the toxin may act on the neurotransmitters that control the glow. But it is quite possible that the venom directly affects the “flashlight” itself. For example, it may deprive it of oxygen, without which the biochemical reactions necessary for the glow do not occur. To draw final conclusions, scientists will need additional research.
Spiders sometimes create a “scarecrow” from their prey
One might assume that the spider does not actually use the fireflies as “bait” for its fellows. Perhaps Abscondita terminalis switches off one “flashlight” as a response to stress and danger. However, this contradicts the behavior of the spider itself, which left the flashing fireflies alive and ate those with painted “flashlights”. This suggests that the spider does use insects for its own purposes.
Some spiders create a “scarecrow” for predators from their prey. Photo source: elementy.ru
It should also be noted that some other spiders also use prey for purposes unrelated to nutrition. For example, orb-weaver spiders of the genus Cyclosa build a large spider from dead insects and debris in the center of their web. True, it does not serve as bait, but rather as a “scarecrow” for predators. But using live wriggling insects to lure more of their fellows is a completely different level of “villainy”, which scientists have learned about for the first time.
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Finally, let us recall that not long ago scientists made other interesting discoveries about spiders, for example, they found out that they most likely dream. And some spiders change the composition of their venom depending on their mood, and we are talking about a species that is considered one of the most deadly.