Encounters between bombardier beetles and two species of toads (Bufo americanus, B. marinus): Speed of prey-capture does not determine success

Summary

The contribution of prey-capture speed to toads' ability to ingest chemically protected prey is evaluated: first, by measuring the speed of toads ingesting palatable prey for comparison with reaction times for prey defenses, and second, by analyzing encounters between toads and bombardier beetles — insects with a quick and potent chemical defense.

• 1.a. Analysis of filmed (64 fps) prey-capture sequences reveals that the rapid tongue flip is preceded by a slower forward lunge of the entire body and followed by a still slower ingestion of retrieved prey (Fig. 1, Table 1). Only the tongue flip, which establishes contact with the prey and retrieves it into the toad's mouth, requires less time than latencies typically reported for invertebrate defensive responses. Ingestion of retrieved prey is not completed until more than 500 ms after initial contact between tongue and prey, giving prey sufficient time to respond with chemical defenses.

• 1.b. Marine toads, the larger of the two species studied, are slower than American toads in all phases of prey-capture up until the beginning of swallowing; however, they complete ingestion as quickly as American toads (Fig. 1, Table 1).

• 2. American toads which attack bombardier beetles usually reject the beetles after retrieving them into their mouths (Table 2). Rejection is a dramatic reversal of prey-capture which typically begins within 300 ms of initial contact between tongue and beetle (Figs. 1, 2). After rejecting a bombardier beetle, American toads exhibit behavior that suggests discomfort and display a temporary aversion to striking again at the beetle (Table 3).

• 3. Marine toads which attack bombardier beetles usually ingest the beetles without showing discomfort (Table 2). When they do reject bombardier beetles or show other behavioral reactions, the behavior is similar to but less intense than that of American toads. Irrespective of the outcome of a previous encounter, marine toads strike willingly when a second bombardier beetle is offered (Table 3).

• 4. An ingested bombardier beetle occasionally causes a toad discomfort but rarely induces the toad to evert its stomach and reject the beetle.

• 5. It is concluded that bombardier beetles attacked by a toad must deploy their chemical defense while still in the toad's mouth if they are to survive. When adequately stimulated, the beetles are able to respond in less time than toads require to ingest prey. Nevertheless, toads can overcome this chemical defense by retrieving and swallowing beetles without eliciting defensive discharges.