Thai biologists are very worried after finding deadly Australian box jellyfish in the seas around Thailand for the first time. The biologists are asking Australian scientists to help them. Box jellyfish are best known for their very powerful venom. Two kinds of box jellyfish are the most venomous creatures in the world. Their stings are very painful and can kill people. Six-year-old Australian Lewis Jones was stung by one of the jellyfish in Trat province on the Gulf of Thailand in December. The boy's heart stopped for two minutes. In April, a 10-year-old Swedish girl died after being stung off the town of Krabi. Thai scientists asked local fishermen to help them. The fishermen trapped some of the jellyfish near Krabi in August. More box jellyfish were caught off Phuket in July. They were taken to the Phuket Marine Biology Centre. But an official at the centre said those jellyfish were not thought to be the deadly kind. Pieces of the jellyfish were sent to Australia to make sure. The official said he hoped that if people knew there were deadly jellyfish in the sea they would be more careful. The box jellyfish are pale blue or have no colour. They have up to 15 tentacles. Their bodies have four sides like a box. They feed on small fish and crabs.