The world of spiders is teeming with fascinating adaptations and behaviors. While most spiders are known for their predatory nature, there are a few remarkable exceptions that have evolved unique dietary preferences. Let’s delve into the intriguing world of three spider species with unusual diets: the vegetarian Bagheera kiplingi, the vampire spider Evarcha culicivora, and the woodlouse-eating Dysdera crocata.
The Vegetarian Spider
Imagine a spider that prefers plants over insects! Bagheera kiplingi, a jumping spider found in Central America, is the closest we’ve come to a vegetarian spider. While it may occasionally supplement its diet with nectar, ant larvae, and nectar-feeding flies, the majority of its meals consist of Beltian bodies, the protein-rich tips of Vachellia acacia shrubs. This spider is so reliant on these Beltian bodies that it lives only in areas with Vachellia plants, and its geographic range is limited by the presence of this specific plant.
But why would a spider, known for its predatory instincts, choose a plant-based diet? It all comes down to mutualism. The Vachellia acacia shrubs have a symbiotic relationship with ants, offering them nectar and Beltian bodies as a reward for protecting them from herbivorous insects. Bagheera has cleverly exploited this relationship, harvesting the Beltian bodies and nectar without providing any defense in return. However, it seems to avoid confrontations with the ants, unless it’s strategically stealing a larva from one.
Bagheera’s unusual diet highlights the incredible adaptability of spiders. While they cannot ingest solids, they have developed a way to break down the Beltian bodies enzymatically within minutes. This plant-based diet accounts for a significant portion of its sustenance, making Bagheera a remarkable outlier in the world of spiders.
The Vampire Spider
Moving on to a spider with an even more peculiar diet, we have Evarcha culicivora, aptly nicknamed the ‘vampire spider’. This spider doesn’t directly feast on human blood, but it indirectly benefits from it by preying on blood-fed female Anopheles mosquitoes. Anopheles mosquitoes are notorious carriers of malaria, and Evarcha actively hunts them down, specifically targeting females that have recently taken a blood meal from humans.
This preference for blood-fed mosquitoes seems to be driven by a unique sexual selection strategy. By consuming these mosquitoes, the spiders acquire a ‘perfume’ that attracts potential mates. This makes their prey preference not only a matter of survival but also a crucial element in their mating rituals. Furthermore, E. culicivora might play a minor role in reducing the transmission of malaria by preventing infected mosquitoes from biting and infecting other individuals.
Evarcha exhibits a clear hierarchy of prey preferences, with blood-fed female Anopheles topping the list. It uses visual cues to identify its preferred prey, recognizing their specific resting posture and assessing the fullness of their abdomen as an indication of a blood meal. The spider even differentiates between male and female mosquitoes based on their antennae, which are more feathered in females.
Interestingly, Evarcha’s prey preference is affected by the presence of Lantana camara shrubs, where mosquitoes often rest and feed on nectar. While the spider also feeds on Lantana’s nectar, the dominant volatile compound of the plant, β-caryophyllene, hinders the spider’s ability to visually assess its prey, potentially leading to misidentification.
The Woodlouse-Eating Spider
Last but not least, we have Dysdera crocata, a spider that specializes in hunting woodlice, also known as isopods. Woodlice are terrestrial crustaceans with a tough, protective carapace. They often roll into a ball or cling to surfaces for defense. This armored exterior and their noxious secretions make them a challenging prey for most predators.
Dysdera crocata, however, has evolved unique adaptations to overcome these challenges. Its chelicerae, the fangs used for biting and grasping prey, are specially modified for hunting woodlice. There are three distinct tactics used by Dysdera species, each associated with specific chelicerae morphology:
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Pincer:
Species with elongated chelicerae, like D. crocata, use the pincer approach, rapidly penetrating the unprotected underside of a woodlouse before it can roll up. They hold the armored side to keep the prey in place, waiting for another opportunity to strike if the woodlouse manages to defend itself.*
Fork:
Species with chelicerae featuring a concave upper surface employ the fork tactic. They quickly grab the woodlouse with their legs, slip their chelicerae underneath, and bite the underside before it can roll up.*
Key:
Spiders with flattened chelicerae use the key tactic. They slide one chelicera between the woodlouse’s armored segments, inserting their fang to deliver a bite.While not all Dysdera species exclusively consume woodlice, the specialized chelicerae and the preference for this prey suggest a metabolic need for this food source. Their ability to extract essential nutrients from woodlice is further correlated with the degree of modification in their chelicerae.
These three extraordinary spider species showcase the remarkable diversity and adaptability within this group of arachnids. Their unusual diets, from plants to blood-fed mosquitoes to woodlice, demonstrate the incredible evolutionary strategies that have allowed spiders to thrive in diverse environments across the globe.
