A shopper got an unexpected freebie with her bananas when she discovered an egg sac thought to be from a venomous South American spider.

Pauline Smith, 51, said she bought the bananas from Aldi in Montrose, Scotland, and was about to drive them home when she noticed something strange.

The specific genus, Acanthoctenus, comprises 13 species from Central and South America. The British Arachnological Society agreed it was a likely candidate. Though the deadly Brazilian wandering spider is part of the same family, Acanthoctenus venom poses no threat to humans.

She said: "When I was putting my shopping into the car, I noticed debris stuck to the banana, and on taking a closer look, I realised it was spider silk with bits of leaf. Then I spotted the small mound of eggs."

She continued: "On returning home, I was excited to look at the nest and eggs in more detail using a hand lens and microscope, and I took some photos.

"Sadly, I also found a squashed hatchling spider when I looked more closely under the microscope. I assume some eggs had hatched, with the remaining eggs being non-viable."

Searching for answers, Pauline shared her photos with a spider group on Facebook.

She said: "It is a very large group, and its members include experts, keen enthusiasts and also those trying to overcome their fear of spiders. Almost immediately, I had an ID of one of the arboreal wandering spiders."

Media officer Meg Skinner said: "Based on the photos provided, we wouldn't confidently be able to identify this to species level, but Acanthoctenus does seem likely. Some spiders do lay eggs on bananas, many will carry egg sacs with them.

"The main species that makes headlines is the Brazilian wandering spider which is of medical significance and rarely found on imports. These have huge egg sacs and are rainforest specialists in Brazil."

Spider expert Paul Hillyard, former curator at London's Natural History Museum, said: "The families known for attaching their egg sac to a banana are harmless to humans. These small spiders sometimes build their nest on a banana because the fruit provides a safe and shady location close to the tiny fruit flies upon which the spiders feed. The spiders have no interest in the banana itself."

Dr Smith, from St Cyrus, kept the affected banana in a secure container, and ate the rest of the bunch. For her, the encounter was an educational one.

She said: "I was fascinated and excited, as it was a great opportunity to learn more about nature, and to have a closer look at how the nest was constructed and the details of the eggs.

"I was also sad imagining the amount of time the spider would have taken to create the perfect nest to protect her eggs as they developed, only to have her efforts wasted."

An Aldi spokesperson emphasised various measures taken to prevent stowaways on bananas, including washing and submerging the fruit.

They said: "While it is extremely rare for naturally-occurring foreign bodies like this to be found on fruit, it can happen in exceptional circumstances due to outdoor growing conditions. However, we want to reassure our customers that this type of spider is harmless and poses no risk to their safety."