Photo: Phidippus species Jumping Spider, Judy Gallagher
Judy Gallagher is an ASNV board member and a regular surveyor of local wildlife who also captures photos of what she sees, in particular the less common species.
Insects protect themselves from predation in a variety of ways, but one of the more unusual techniques is to resemble the predator that they want to avoid. Several insects mimic the appearance of jumping spiders, formidable predators for their size. As the mimicry patterns are only in certain parts of the imitators’ bodies, this is called partial mimicry.
Peacock Brenthia metalmark moth, Judy Gallagher
Metalmark moths in the genus Brenthia mimic jumping spiders. Their posture and wing markings make the moth look a little like a head with jumping spider-like eyes, and the moth moves with short bursts of movement, just like a jumping spider would. The jumping spider resemblance is not terribly obvious to me, and even if it were, it’s more important that the spider sees the resemblance. So, scientists conducted experiments with the moths, placing them with jumping spiders in an enclosed space. The spiders displayed territorial behaviors, implying that they thought the moths were jumping spiders. They did not do this with other similarly sized moths that lacked jumping spider markings. While the spiders were busy displaying territorial behavior, the moths flew away. In the study, most metalmark moths survived, and most other moths did not.
Red-banded Hairstreak, Judy Gallagher
Some butterflies also mimic jumping spiders. The Red-banded Hairstreak has spots and tails on its wings that look like a jumping spider’s head, and the way it moves its wings mimics jumping spider movements. In an experiment, a Red-banded Hairstreak was placed in an enclosed space with a jumping spider. The spider attacked what it thought was the head of its prey and directed its venom there to paralyze it. The Red-banded Hairstreak flew away every time, although it sometimes incurred minor wing damage. Eleven other butterfly and moth species without jumping spider markings were exposed to the jumping spider, and many of them succumbed to the spider’s attack.
The jumping spider grew tired when attacking prey that it could not capture. That could potentially lead it to not attack the butterfly at all.
Red-banded Hairstreak with wing damage, Judy Gallagher
There are other Hairstreaks with spider-like markings, and an examination of museum specimens shows that the more deceptive-looking the markings are, the more frequently they are found to be damaged. If the Jumping Spider does attack the butterfly, it targets the false head markings on the wings. The butterfly incurs wing damage, but it escapes without damage to its vital organs.
Gemmed Satyr, Judy Gallagher
The Gemmed Satyr butterfly has a perfect picture of a jumping spider on its hindwings, but I was unable to find any studies that documented interactions between the species.
Pepper Maggot showing "spider leg" wing markings, and “spider eye” thoracic markings, Judy Gallagher
Some flies mimic jumping spiders. The Pepper Maggot (Isn’t that a great name!?) has a leg-like pattern on its wings. It waves its wings in a way that mimics the territorial displays of jumping spiders, and the thoracic markings look a little like a spider’s head with eyes. When faced with this fly, jumping spiders display territorially and then retreat. In a gruesome experiment, scientists transplanted house fly wings onto the Pepper Maggot, who was then successfully attacked by the jumping spiders. House flies with Pepper Maggot wings were also attacked, showing that the fly needs both the wing markings and the wing waving behavior to avoid jumping spiders.
Rhagoletis species Fruit Fly, Judy Gallagher
Scientists originally thought that Rhagoletis species Fruit Fly markings were species-recognition marks, but it turns out that these also mimic jumping spiders. When a jumping spider approaches the fly, the fly spreads its wing and wobbles from side to side. This looks similar to jumping spider movements. The spider is intimidated and it leaves the fly alone. Scientists experimented by painting the fly’s wings black so that the spider pattern was no longer there, and the jumping spider then attacked the fly.
Phidippus species Jumping Spider, the model, Judy Gallagher
It's hard for me to decide whether I am more impressed by how moths, butterflies and flies have evolved to outwit jumping spider predators, or by the experiments that scientists have come up with to test this. In either case, it is clear to me that sometimes the best defense is a good offense.
View more of Judy’s Observations from Meadowood articles here.