If it were me, I'd take the plant back. Spider mites on English ivy are enough of a pain to deal with (especially in winter) that I don't think it'd be worth your time to try to fix this.

(And I say the above as someone who has tried to get mites off of an English ivy, in my home, during the winter. I didn't get the mites off, and I pretty well destroyed the plant in the process of trying.)

The terrarium thing might work, but it's not like humidity kills mites; it just slows them down. Also the lack of air circulation in the terrarium might encourage them as much as the humidity discourages them and you'd just break even.

Thanks for the advice. I'm sure you're right about returning it, I didn't realise spider mites were such an issue with English ivy.

Is there another vine-type plant you can recommend that won't attract the spider mites?

Thanks, Sara.

Ivy are spider-mite magnets. If you really want the plant you can wash it off thoroughly and spray the living beans out of it with Ortho Systemic. It works like nothing else I ever tired. To avoid chemicals you can try Neem oil. Make sure you drench the undersides of the leaves no matter what you use. And repeat the spray in a few days or a week to get the little monsters you missed the first time. Meanwhile as you know, keep it away from other plants. Remember, you can spread these mites on your hands and clothes also.

Ivy-like plants that are less prone to spider mites. Hmmm. Well,

Senecio macroglossus (cape ivy) looks very much like English ivy (Hedera helix), and isn't particularly attractive to mites, but it has a whole set of other problems that don't make it significantly easier, and it's not all that widely available.

Hedera canariensis (Algerian ivy) looks like a very big version of H. helix. It's not as attractive to mites, but you still have to watch carefully for them (I recently lost my plant to mites because I didn't notice quickly enough what was going on.): once they get going, the population explodes like it would for H. helix.

I'm not hugely familiar with Ficus pumila (creeping fig), but I've seen some varieties of it that had a similarly-sized leaf: the effect from a distance is kinda the same. There's also a (smaller-leaved) version with white around the leaf edges, but I think that may be the only variegation option. I'm under the impression that they're fairly easy plants, and while mites are possible, they should be more easily controlled. I have not yet tested this by trying to grow it personally.

Plectranthus nummularius (Swedish ivy) trails, though it doesn't much resemble English ivy otherwise. It's good about bugs: I've had one for a while that has never had any problems, even when other plants in the vicinity did.

Pilea nummularifolia is another trailer that looks even less like Hedera helix than Plectranthus nummularius does. Nice plant, though. I'm actually getting to be pretty fond of mine. Don't really know on the bug situation, but again, no problems for mine so far.

Cissus rhombifolia (grape ivy, oakleaf ivy) vines and trails. Doesn't look much like English ivy, and it is supposed to have some issues with mites, but it exists, and I've had mine over a year and it's been very civilized.

Zebrina pendula (wandering Jew) and Tradescantia pallida (purple heart) are pretty pest-free in my experience, though they get leggy quickly and also bear no resemblance whatsoever to English ivy except for trailing.

Epipremnum aureum (pothos) is almost too obvious to be worth mentioning. Ditto Philodendron hederaceum (heart-leaf philodendron) and the other climbing Philodendrons. Philodendron hederaceum in particular is underrated, in my opinion, because it will tolerate a lot of abuse, and so the plants everybody always sees are plants that have been through a lot of abuse, which makes them not look so great. A well-grown P. hederaceum is a thing of beauty. All three are decent if not spectacular when it comes to bugs.

Hoya carnosa, again, doesn't look like English ivy, and some people have trouble with them, but mine have been great so far, and are very easy-maintenance. Spider mites aren't a problem with Hoya spp. so much, but mealybugs can be huge, so it's important to pick your plant out very carefully. But mealybugs aside, you could do worse.

This wasn't an exhaustive list, but, you know, we could be here all day. I hope there's something in there that's useful to you.

There's also Scindapsus, it needs bright indirect light and shouldn't be allowed to go dry, like you can get away with the pothos or epripmemnum. Also slow growing (for me) so you'll need to be patient.

Several years ago, in anticipation of an in-city move and wanting to keep my plants from getting harmed from someone carefully moving them, I stored them at a friends house, 2 ivies and several other smaller plants, all grouped together tightly in a shallow box. Friend kept them together for a month, then gave back to me. The ivies looked funny, faded almost, and then upon closer examination I realized they were loaded with spidymites! None of the other plants in the box with these 2 ivies were affected.

I ended up taking cuttings that I could dunk completely in dishsoap/alcohol every 3-5 days, did that 3 or 4 times, and have not had a reoccurence of those type of bugs since. What I read when researching them on the net is that spider mites can hibernate in our homes when conditions aren't good, like in cracks of woodwork and such, and then come out and attack when indoor conditions become favourable. Don't know if this is actually true, and we've moved again since, and my ivies are spidy free!