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The notion of spiders using ants as bodyguards seems a bit contradictory, but that is exactly what occurs on the tropical forest floors of the Philippines. The jumping spider (Phintella piatensis) strategically nests within the vicinity of the aggressive Asian weaver ant (Ocecophylla smaragdina) as a defense tactic against its main predator, the spitting spider (Scytodes species). The behavior of a vulnerable species seeking protection of a different, more aggressive species is commonly seen among birds, but not among arachnids. In a recent study published in Behavioral Ecology and Social Biology, researchers Ximena Nelson of the University of Canterbury in New Zealand and Robert Jackson of Canterbury and the International Centre of Insect Physiology and Ecology in Kenya examined this dynamic relationship between the protective weaver ant, the timid jumping spider, and the predatory spitting spider.
Jumping spiders are the main prey for spitting spiders. The spitting spider is a lethal hunter that, from a distance, shoots a sticky gum from its fangs onto its prey. The prey is rendered immobile just long enough for the spitting spider to inject it with venom and wrap it in silk. In the Philippines, the spitting spider and jumping spider inhabit the same large, waxy leaves. The spitting spider often spins its web directly above the nest of a jumping spider, allowing it to capture the jumping spider as it leaves or enters the nest. However, the researchers found that spitting spiders avoid building their webs above jumping spider nests when weaver ants are present.
A spitting spider (Philippine Scytodes) about to feast on a jumping spider. Photo by Ximena Nelson.
A spitting spider in its web hovers above a thin jumping spider nest. Photo by Ximena Nelson.
At the International Rice Research Institute (IRRI) in Los Baños in the Philippines, Nelson and her team conducted a series of experiments examining how the sensory characteristics of jumping and spitting spiders influenced their behavior. They hypothesized that the jumping spider uses predominately its eyesight when choosing nesting locations close to weaver ants whereas the spitting spider uses its olfactory senses to avoid weaver ants. The researchers placed jumping spiders and spitting spiders in different chambers and observed whether the visual presence or odor of weaver ants triggered nest-building or web-spinning.
The researchers observed that the jumping spiders relied heavily on visual cues when choosing where to build nests, and that 92 percent established nests when weaver ants were visible. They were also more likely to build nests when only the scent of weaver ants was present, although scent proved to be less influential than sight. To test whether the specific presence of weaver ants or the general presence of other insects evoked nest building, leafhoppers were also placed in chambers with jumping spiders. The presence of leafhoppers had a slight effect on jumping spider activity, with 68 percent of the jumping spiders choosing to build nests.
Conversely, web-building behavior in spitting spiders was influenced much more by odor rather than the visual presence of weaver ants; 85 percent of the spitting spiders built a web when an occupied jumping spider nest was present in the chamber. However, when occupied jumping spider nests and the scent of weaver ants were both present, only 12 percent of the spitting spiders spun a web. On the other hand, when an occupied jumping spider nest was present and ants could be seen but not smelled, 80 percent of the spitting spiders built webs.
 A weaver ant nest in Thailand. Photo courtesy of HAH. |
Spitting spiders use their sense of smell rather than sight when choosing strategic nesting locations and when hunting jumping spiders. In the field, the researchers observed 174 instances where spitting spiders spun webs directly above jumping spider nests. In all of these cases, weaver ants were never present on the inhabited leaves nor within the vicinity.
The presence of weaver ants elicits two very different responses from the predator-prey duo of the spitting spider and jumping spider. By using their eyesight and olfactory senses, jumping spiders seek protection under weaver ants by building nests in their presence, and their ant-proof nests allow them to live in relative safety among weaver ants. In contrast, the lethal spitting spider uses its olfactory senses to help it locate prey as well as avoid its foes.
While this is an unusual instance of a spider seeking the protection of another arthropod species that is also a potential predator, other multiple-species associations in which one species seeks the protection of another has been commonly observed within the jumping spider family.
“There are other salticids (members of the jumping spider family) that form mixed-species associations with other species of salticids (especially in Africa), and we think this might be a response either to ant predation, or to the presence of ants,” Nelson told mongabay.com. “Other salticids sometimes aggregate in the vicinity of weaver ants nests, but here they seem to form crèches to protect their young, as adults are better able to defend themselves than the young.”
This study could contribute to a more thorough understanding of arthropod relationships that occur in the microhabitats of tropical rainforests. The researchers believe other associations similar to the dynamic between weaver ants and arachnids could potentially be found among other arthropods.
Citations:
- Nelson, Ximena J., and Robert R. Jackson. “Anti-predator Crèches and Aggregations of Ant-mimicking Jumping Spiders (Araneae: Salticidae).” Biological Journal of the Linnean Society 94.3 (2008): 475-81.
- Nelson, X.J. & Jackson, R.R. (2014). Timid spider uses odor and visual cues to actively select protected nesting sites near ants, Behavioral Ecology and Sociobiology. DOI 10.1007/s00265-014-1690-2
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