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Picture yourself as a spider nestled in a tangled web, hidden within a decaying log in a damp Hawaiian forest. Your existence revolves around catching unsuspecting insects, which you subdue with venom and wrap for later consumption. Life may seem uncomplicated in this picturesque jungle, yet there’s an unsettling change stirring within your serene routine.
You have begun to experience moments of confusion and disorientation. Occasionally, a vibration draws you closer, only for you to discover remnants of your own previously shed exoskeleton or the remains of a meal you can’t distinctly recall consuming. Trash accumulates in your corner that you could have sworn you didn’t leave there. And then there are those times when you return to a freshly liquefied prey only to find large parts of it missing—consumed, yet the details of the meal escape your mind. You could be losing your edge, feeling your mental acuity deteriorate like the soft remnants of your former meals.
But chances are, you’re not losing it. Instead, you may be sharing your habitat with a peculiar newcomer: a moth species recently identified for its extraordinary behavior during its caterpillar phase. This creature, nicknamed the “bone collector,” resides within your web, expertly camouflaging itself using the discarded remains of other insects. This astonishing discovery, highlighted in a recent study published in the journal Science on April 24, presents new questions about the lives of creatures living alongside one another in such ecosystems. “What’s remarkable is its unique behavior,” explains Daniel Rubinoff, the lead author of the study and entomologist at the University of Hawai’i at Mānoa.
A Flair for Fashion
At first glance, the bone collector caterpillars appear rather unremarkable—stout, pale, and roughly five millimeters in size. The adult moths maintain a similarly plain appearance, noteworthy primarily for the subtle patterns of white spots set against their gray forewings.
However, once the caterpillars adorn themselves, their true uniqueness emerges. They commence by spinning a silk case, akin to other members of the genus Hyposmocoma. Carefully navigating their spiderweb environment, they selectively scavenge various insect parts, ensuring that they only incorporate high-quality remains into their protective disguise.
[ Related: Baby hummingbird appears to mimic caterpillar to avoid death.]
Unlike typical scavengers, these caterpillars meticulously assess each potential addition to their collection. “They examine everything that crosses their path,” notes Rubinoff, explaining that they use their jaws and legs to inspect insect remains, determining which parts to integrate into their growing assemblage. Remarkably, they are so focused on amassing these trophies that when given alternative materials in laboratory settings—like leaves or soil—they ignore them in favor of their preferred scavenging. Dressed in their dramatic ensembles, they are now skilled actors, slipping through spiderwebs undetected and capable of feasting on both live and recently deceased captive insects. Even cannibalism within their kind is not off the table; only one bone collector may thrive within a single web.
Hunting for a Hunter
Instances of carnivorous caterpillars are exceedingly rare. Within the nearly 200,000 documented species of moths and butterflies, a mere 0.13 percent are known to feed on flesh. None exhibit the same behavior as the bone collectors, who inhabit spider webs and use only human remains for their cases.
Initially, Rubinoff and his team were taken aback by their observations, suspecting it might have been an isolated incident. “We wondered if it was a unique caterpillar making unusual choices for its case,” said Michael San Jose, a co-author of the study. Their skepticism persisted until extensive surveys over two decades began to reveal these remarkable larvae, often cloaked in skeletal adornments, positioned as predators in environments typically dominated by prey.
“It was less a sudden realization, more of a gradual understanding,” Rubinoff recounted. “It’s a peculiar feeling to come to a conclusion that defies all expectations.”
So far, scientists have documented 62 individuals of this species inhabiting a single mountainside in the Wai’anae Range of Oahu. Searches in surrounding areas have yielded no further findings, suggesting that the bone collectors are confined to a scant six square miles of forest. This isolation places them at immediate risk of extinction, a scenario that Rubinoff warns is perilously near.
Bone Collecting is a Lonely Life
The Hawaiian Islands boast a diverse array of endemic species, including those from the genus Hyposmocoma, which are unique to this region. Unfortunately, the introduction of various invasive species has drastically altered these ecosystems, posing a considerable threat to the continued survival of native species. Although bone collectors have been observed in webs constructed by invasive spiders, their elusive nature raises the possibility that their native host species has diminished significantly, potentially facing extinction.
Moreover, climate change is forcing shifts in habitat suitability, which may further jeopardize the bone collectors. These caterpillars seem to prefer specific altitude zones within their mountainous habitat, and changing temperature and rainfall patterns could reduce the range where they can thrive, cautions San Jose. “We are observing a system as it faces eradication,” he notes. The disappearance of these unique caterpillars not only signifies the loss of an intriguing species but also impacts the broader ecosystem relied upon by both wildlife and humans for clean air and water.
Using some of the collected caterpillars, entomologists have reared them in controlled settings to collect behavioral and genetic data by introducing various prey and environments. Through DNA analysis, researchers have confirmed that bone collectors represent a distinct lineage within the Hyposmocoma family tree, and they appear to be the last surviving representatives of this ancient group. Their nearest genetic relatives, which are also carnivorous builders, diverged from the bone collectors over five million years ago, predating the island’s current geological formation.
It is likely that these remarkable caterpillars originated on Kaua’i or another now-eroded volcanic island and made their way to Oahu serendipitously, relying on wind or ocean currents to reach their current isolated habitat. “The evolutionary journey of these bone collectors spans millions of years, making them incredibly rare,” Rubinoff states. It is crucial to safeguard their existence. Ironically, for the spiders, they might just prefer a more solitary life.
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