The Joro spider ( Trichonephila clavata), a striking arachnid native to East Asia, has recently become an invasive species in the United States. While its appearance may be alarming to some, understanding its diet and behavior can help dispel misconceptions and foster coexistence. This article provides a comprehensive overview of the Joro spider's dietary habits, exploring how its food choices relate to its size, sex, and impact on the environment.
Introduction
The Joro spider, named after a Japanese folkloric "spider demon," has captured attention not only for its vibrant colors and large size but also for its expanding range. Originally found in Japan, Korea, Taiwan, and China, it was likely introduced to the United States around 2013 via shipping containers. Since then, it has thrived in the Southeast, raising questions about its ecological impact, particularly its dietary habits.
Joro Spider: An Overview
Taxonomy and Appearance
The Joro spider belongs to the genus Trichonephila, characterized by spiders that create woven orbs for their webs. The name Trichonephila clavata was assigned by Friedrich Dahl in the early 20th century. In Japan, it is known as "jorōgumo," also the name of a mythical creature from the Edo period.
Female Joro spiders are significantly larger than males, ranging from 1.7 to 2.5 cm (0.67-1 in) in body length, with some reaching 7.6-10.16 cm (three to four inches) in diameter in Georgia. They exhibit striking coloration with gray and dark blue stripes and a red belly. Males, on the other hand, are brown and plain, measuring only 0.7 to 1 cm (0.27-0.39 in).
Habitat and Spread
The Joro spider's primary habitat is in Southeast Asia, preferring humid environments in Japan, China, Taiwan, and Korea. Since 2013, it has become an invasive species in the United States, particularly in Georgia and South Carolina, with potential to spread further along the East Coast. Its dispersal is facilitated by ballooning, where spiderlings use silk threads to catch the wind and travel long distances.
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Dietary Preferences and Hunting Strategies
Carnivorous Diet
Joro spiders are carnivorous, requiring the protein and nutrients from insects to maintain their health. They are opportunistic feeders, preying on a variety of insects that become ensnared in their webs.
Web Construction and Prey Capture
Joro spiders are orb-weavers, constructing large, three-layered webs that can be up to 10 feet wide. These webs, often tinted gold in sunlight, consist of a central orb with irregular layers in front and behind it, creating a complex, three-dimensional structure. The webs serve as effective traps for flying insects.
Common Prey Items
The diet of Joro spiders typically includes mosquitoes, yellow jackets, stink bugs, beetles, bees, and biting flies. They are passive hunters, waiting for insects to become entangled in their webs before wrapping them in silk and using venom to subdue them. Studies have also recorded them preying on spotted lanternflies, an invasive species in the northeastern United States.
Sex-Specific Dietary Patterns
Research indicates that dietary patterns in Joro spiders may be sex-specific and related to body size and condition. A study combining morphometric size analysis with molecular gut content analysis via DNA metabarcoding and high-throughput sequencing revealed differences in the diets of male and female Joro spiders.
Female Diet Diversity
Female Joro spiders are larger than males and exhibit more diverse diets. While both sexes consume the same prey taxa, females have been found to consume more than 50 additional taxa, leading to significant dissimilarity in prey composition between sexes.
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Male Diet and Body Size
As male body size increases, diet diversity and body condition tend to decrease. This suggests a potential trade-off between time spent foraging and actively defending their position on the web to mate with females. Male and female spiders captured from the same web share prey taxa, but the proportion of prey overlap is not related to male size.
Interaction with Monarch Butterflies
Unpalatability of Monarchs
Monarch butterflies, which feed on milkweeds as larvae, sequester cardiac glycosides into their adult tissues, making them unpalatable to many predators. An interesting question arose regarding whether Joro spiders, which do not coexist with monarchs in their native range, would recognize this unpalatability.
Avoidance Behavior
Field trials involving tossing monarchs into Joro spider webs revealed that the spiders avoided eating monarchs. Joro spiders only attacked monarchs 20% of the time, significantly less than the attack rates on gulf fritillaries (86%) and tiger swallowtails (58%). Some Joro spiders even removed monarchs from their webs. These findings suggest that Joro spiders can recognize monarch butterflies as being unpalatable, even without prior experience with the species.
Comparison with Native Spiders
In contrast to Joro spiders, native garden spiders ( Argiope aurantia) readily attacked monarchs in similar field trials. This suggests that native spiders may have learned to consume monarchs, possibly by avoiding body parts with high concentrations of cardenolides.
Ecological Impact
Impact on Native Species
As an invasive species, the Joro spider's impact on native ecology is still being studied. There is concern that they might compete with native spiders for food or displace them. However, some entomologists believe their ecological impact will be mild.
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Beneficial Role in Pest Control
Joro spiders can help control populations of invasive species like stink bugs and spotted lanternflies. By preying on a variety of flying insects, they contribute to natural pest control and help maintain ecological balance.
Management and Prevention
Minimizing Nuisance
While Joro spiders are not dangerous to humans, their large webs can be a nuisance. To prevent them from settling in yards or around homes, consider the following tips:
- Watch your landscaping: Rich vegetation against your house could encourage Joro spiders to settle there.
- Don't leave outdoor lights on: Bright lights attract insects, which in turn attract Joro spiders.
- Eliminate hiding places: Remove potential web-building sites by regularly trimming vegetation.
- Remove webs: Use a broom or cobweb brush to remove Joro spiders and their webs.
Control Measures
Due to their minimal medical and economic impact, control measures for Joro spiders are generally not necessary. Pesticide applications are not typically required.
tags: #trichonephila #clavata #diet