A hypernym for 'insects', 'worms' and the like

From Oxford:

insect:

any small creature with six legs and a body divided into three parts. Insects usually also have wings. Ants, bees and flies are all insects

Insect is often used to refer to other small creatures, for example spiders, although this is not correct scientific language.

worm:

1. a long thin creature with no bones or legs, that lives in soil

2. long thin creatures that live inside the bodies of humans or animals and can cause illness

3. the young form of an insect when it looks like a short worm

I find both these definitions oddly restrictive. Insects have 6 legs and worms (in the primary sense) have none. The other senses of worm are also specific. There are many small creatures who do not fall into these categories. Centipedes definity have legs, and a lot more than six. Is there a common (not too scientific) word to refer to all small creatures?

A bug doesn't work, as is defined as

chiefly North American A small insect:

a thick green scum which crawls with bugs, centipedes, and worse

Insect, not creature, not worm. Also note the exclusion of centipedes from the umbrella of bugs. In fact, Oxford defines centipedes exclusively in scientific terms.

A predatory myriapod invertebrate with a flattened elongated body composed of many segments. Most segments bear a single pair of legs, the front pair being modified as poison fangs.

Although Oxford here lists an informal sense of insect:

informal Any small invertebrate animal such as a spider or tick.

It curiously drops this definition in the advanced learners' version. Moreover, it's reluctant to use the term in its own definition of spider:

An eight-legged predatory arachnid with an unsegmented body consisting of a fused head and thorax and a rounded abdomen. Spiders have fangs which inject poison into their prey, and most kinds spin webs in which to capture insects.

Questions:

• Is there any word, preferably not too informal, which would include all small creatures like insects, worms, spiders and centipedes; without having to resort to biological jargon?

• Also, how right/wrong is it to use insect or bug for this purpose?

Solution 1:

Small children are easily interested in small creatures and, unsurprisingly, primary schools in Britain find the study of such animals a good starting point for much of the curriculum. However, it is was thought that calling them "creepy-crawlies" would risk alienating pupils and trigger the fear and distaste which was common in their grandparents' day.

So the term for these small creatures most often used in British Primary Education is minibeasts For a general view of UK minibeast history see this wikipedia article.

"Minibeast" or "Minibeasts" is a term for a variety of arthropods and other invertebrates, including spiders, ants, butterflies, bees, wasps, flies, woodlice 1, and many others.

Solution 2:

Creepy-crawlies.

informal
A spider, worm, or other small flightless creature, especially when considered unpleasant or frightening:

^ Covers all three cases.

Also, despite your dictionary defining "bug" as an insect specifically, i wouldn't balk at using it to describe worms or spiders as well.