We were on Bandos 1-8th August last year ironically.
Like you, the pesky little mossies really like me
On Bandos , they spray the island every evening, and although it is quite lush, we were bitten less there than we had been on Meeru the week previously. That being said, we DID use insect repellent in the evenings (not an especially high-dose one though - the kids actually just had the aftersun with repellent in) - standard "jungle formula" did the trick pretty much . We did also have the Raid plug-ins with us which we put on in the rooms (remember that they use the same plug types as here in the UK). The one place on Bandos we all picked up a couple of bites was by the kids playground one early evening when it had just been raining briefly.
I think it is possible that we got bitten more frequently on Meeru as we had the outdoor bathrooms, which obviously you can't keep the bugs out of!
Don't remember seeing spiders of any consequence - a fair few ants around, plus some of the biggest flying beetles I've ever seen (only outside) - plus the usual gekkos (but encourage those as they eat mossies!!!!)
Do try to take reasonable supplies of repellent, suncream and after-bite stuff with you as - like all Maldivian Islands - the gift shop is pretty limited in it's range (although, to be fair the one on Bandos is on 2 floors and easily the biggest shop of the 5 islands we have visited) - it's also quite expensive compared to good old Superdrug!
Shout or pm if you need any further info!!