Sunday, May 12, 2002		Nature

How to confuse predators
Nutan Shukla

MANY prey species avoid predators by confusing them. Sea squids, cuttlefish and octopuses confuse predators by using a cloud of ink. The cloud is usually the same size and shape as the escapee, and serves as dummy prey which the predator often tries to catch. Meanwhile, the cunning cephalopod has changed colour and shot off in another direction, using its water-powered siphon as a means of jet-propulsion.

The art of confusing others can be further enhanced by offering something expendable. Many lizards are able to discard their body parts, for example tail in the case of house lizard, leaving the predator a small meal but allowing the prey a chance to flee and re-grow the lost body parts.

Tropical tiger moths ‘jam’ the sonar system of pursuing bats. The moth emits a burst of ultrasound pulses which startles the bat, just as it is about to attack. Other moths, tuning into the frequencies which bats use for echolocation, take evasive action at the moment of attack. Yet others foil pursuit by simply folding their wings and dropping out of the sky.

Flying fish flee the opposite way. Pursued by tuna or other fast-swimming fish, flying fish leap clear of the water and glide in the air. There are ‘two-wingers’ with enlarged pectoral fins, and ‘four-wingers’ possessing wing-like pectoral and pelvic fins. The total ‘wing’ area is the same, but four-wingers fly slightly further and in rougher sea conditions than two-wingers.

In order to leave the water, the flying fish accelerates towards the surface, breaking through at an angle of about 30 degrees. The wings are expanded and, maintaining the same angle, the tail remains in the water and waggles at 50-70 strokes per second, propelling the fish along the surface. This is the ‘taxiing’ stage, which is followed by take-off. At an air-speed of 49-66 ft per second, a flight of 55 yards can be achieved at a height of 25 ft above the sea’s surface. At this point the fish drops back to the surface, gives another waggle of its tail, and takes off again without submerging. It can travel for about 400 metres in half a minute.

Lizard fish bury into the sand on the seabed to escape predators, and creatures living in deserts, such as lizards, beetles and snakes, adopt the same strategy.

Some butterflies, such as the grayling, have small eyespots on the edges of their wings. This is an attempt to confuse and misdirect the pecks of predatory birds away from the valuable and vulnerable body and focus instead on the less vital wing edge. And judging by the number of butterflies to be seen with triangular chunks taken out of the wing, leaving the body intact and in working order, it is successful.

Other butterflies have false heads, the head being the most vulnerable part of the body and the obvious target for a predator. Some have the head on the wing tips, well away from the real head. Its appearance is enhanced by antennae-like projections and eyespots. One tropical hair-streak even has brown-and-white stripes that direct a predator’s attention directly towards the false head. It even behaves in a way that confuses an attacker. On landing, it turns around and is, therefore, ready to flee in the opposite direction to which the predator expects it to fly.