The large, bulbous spider (which looks remarkably similar to a bird dropping when at rest) emits pseudo pheromones from her body that mimic those of certain groups of moths. Males of those species flutter closer, thinking a female moth is nearby. When one gets in range, the spider flicks that sticky silken droplet on its fishing line of death and snares the hapless creature.
Upon impact, the tightly woven sticky silken ball essentially explodes, further entangling the moth, which is then reeled in and eaten. We actually watched a moth come in, land on the leaf over the spider, then flutter downward at which point the bolas spider began whirling its glue-like droplet at it. It missed, but it was amazing how fast the spider reacted and the rapidity with which it could fling its bolas.
