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Species:

Habitat: originally from , it has been introduced to south-east Asia and the US, where it is considered an

How do you like your eggs? Improved by kisses, , eggs are good eating. They are full of nutrition, and while you might have to get past a parent or two, the eggs themselves don’t fight back.

As a result, all eggs are prime targets at mealtime. Parents may lose over half their ova, unless, that is, they are channelled apple snails, even though their eggs are brightly advertised. This modest animal packs a knockout defensive punch: an enzyme inhibitor that makes the eggs, quite literally, indigestible.

Bright red and dangerous

Channelled apple snails live underwater. is a laid-back affair, typically taking 12 hours but : apparently it takes this long simply to . Satisfied females then crawl out of the water onto plant stems or walls, where they lay their eggs in lumpy clusters. The eggs are a bright, pinkish red, and extremely conspicuous.

Bright colours are often warnings, and in this case the warning is honest. The eggs are laced with a , which has been shown to leaving them weak and staggering. High doses kill mice within 30 hours.

Surely that’s enough of a defence for our lowly snail? Not so fast. PV2 is rather slow-acting and it seems unlikely that by itself it could ensure that the eggs are completely safe. Now Horacio Heras and colleagues of the in Argentina have found that the eggs have a second line of defence.

Don’t eat me!

The answer lies in the colour. It comes from a protein called ovorubin, which is and . This handy protein and . It had also long been assumed to defend the eggs against microbial infections. But when Heras tested it against a range of common bacteria like Escherichia coli and Salmonella, he found it had no effect.

A chemical analysis revealed that ovorubin is a proteinase inhibitor: it blocks the activity of enzymes that break down proteins. Proteinase inhibitors are , which use them to defend themselves against herbivores. Animals that eat too much of the plant find that they are .

It turns out that the eggs use ovorubin in the same way. Ovorubin can bind itself to trypsin, a common digestive enzyme that breaks down proteins. Heras fed rats an ovorubin-enriched diet and found that they grew slower than rats given normal food, though the effect wore off after four days.

Channelled apple snail eggs are the first animal known to deter predators by stopping them digesting their food. Both toxic and indigestible, it’s no wonder that only .

Journal reference:

Read previous Zoologger columns: The hardest bat in the world, Houdini fly inflates head to break walls, A primate with eyes bigger than its brains, The solar-powered electric hornet, The miniature cuckold fish, Lemmings swap suicide for infanticide, The slow-moving mystery of the sloth’s neck, How weakness makes the crayfish stronger , The heaviest animal in the air, Ancient air-breathing, triple-jawed fish, Horror fly returns from the dead