Deanna and Alan Henderson's lives are consumed with "all things buggy".

From providing "bug wrangling" services for international wildlife documentaries to running education programs, even sending live insects in the mail, the Far North Queensland couple and business partners live and breathe invertebrates.

Their business, Minibeast Wildlife, posts about 3,500 parcels every year using Australia Post's automated measuring system.

But the Hendersons say they have been hit with thousands of dollars in incorrect postage charges in the past year, prompting them to lodge a complaint with the Postal Industry Ombudsman.

The most recent was $731.68 for a 300-gram parcel containing praying mantises.

"One of our 33-centimetre parcels came back to us measured-in as over a metre and something like 55 kilograms," Mr Henderson said.

"Australia Post had already charged us for that and popped that $700 fee onto our tab."

Insects are permitted to be sent in the post in Australia.

Red flags

AusPost's automatic size and weight scanning technology has been in use for several years.

It allows MyPost Business customers to skip the queues at post offices by pre-ordering shipping labels and lodging them at red street posting boxes.

Customers must apply the correct postage size and weight for parcels, otherwise they will be charged for "underpaid postage" after the parcel has been sent for delivery.

AusPost's parcel processing machines automatically detect differences between the postage paid and what the correct postage should be.

Ms Henderson said fees automatically deducted from their account started off small, but gradually grew.

"I was like 'woah, hang on a minute, this is not right'," she said.

AusPost apology

The Australian government-owned corporation has apologised to the Hendersons saying the automated system "in the vast majority of cases works well".

"We have been actively working to put in place a tailored solution for the company due to the unusually lightweight nature of their parcels," a spokesperson said.

The Hendersons have lodged a complaint with the Australian Competition and Consumer Commission (ACCC) and the Postal Industry Ombudsman.

The couple said they had received refunds for about 20 incorrect fees, but dozens of others have been rejected due to insufficient evidence.

"We've now had to photograph every single box that we pack and that, again, takes us time."

In 2023-'24 the Postal Industry Ombudsman received 4,056 complaints about AusPost, 55 per cent of which related to domestic parcels and parcel delivery.

The Ombudsman's office told the ABC its records showed 12 complaints last year financial year were specifically about Dimension Weight Scanning (DWS) calculations.

But it cautioned that it may have received more complaints about DWS that were lodged under different categories.

Professor of artificial intelligence at UQ's School of Electrical Engineering and Computer Science, Tim Miller, said automated systems such as DWS would never get it right all the time.

"Something like that, that might measure a package size, you could probably go from getting it right 95 per cent of the time, but if done poorly it could be 50, 60, 80 per cent of the time," Professor Miller said.