The mystery of crop circles which have appeared from time to time in and around Tasmania's legal opium poppy fields may have been solved.

It seems it is not aliens, but junkie wallabies hopping around in dazed circles - perhaps.

Poppies are grown in Tasmania for morphine that is used by the pharmaceutical industry to make pain control drugs.

But it appears humans are not the only ones who have discovered that the poppies contain narcotics.

Recently retired farmer Lyndley Chopping spent more than 30 years growing poppies and he has seen wallabies acting strangely in his fields.

"They would just come and eat some poppies and they would go away. They'd come back again and they would do their circle work in the paddock," he said.

"They seem to know when they've had enough. They'll still be around and they would leave them alone. It's hard to work out. Didn't seem to be any real pattern to their behaviour."

But the state's largest poppy producer, Tasmanian Alkaloids, has noticed a pattern in the wallabies' behaviour.

Rick Rockliff is the company's field operations manager.

"Often other forms of food are in short supply in late January/February and poppy capsules, half their weight is actually seed which is very nutritious. It's a seed you see on bread rolls and in bread mixtures and things like that," he said.

"But in the process of eating open the capsule it's quite possible they do ingest a little bit of the capsule material that does contain the alkaloids and this can have some short-term effect.

"They are, after all, a narcotic and ingested in big amounts it can have an effect."

But a wildlife vet isn't sure that the wallabies are getting stoned. Barry Wells is the animal welfare officer at the University of Tasmania.

"It's quite possible that they are being affected by them but other things can do it too," he said.

"So I guess we need to rule out the other things or need to look at this more closely to make sure that it is affecting them, that they are eating lots of it.

"I mean, I would expect that they, if they are they could very well become addicted and start eating lots of them. But that remains to be seen I guess."

He says if the wallabies are getting addicted to the poppies there would probably be signs, like bowel upsets and constipation.

"We would [also] expect to see them being incoordinate - that is they might stagger about, they might walk in circles," he said.

"They might just be acting in what would appear to be a lethargic way and certainly out of character from what you would expect with wild wallabies."