Probably one of the tussock moth species.

Fridges with water lines (ice makers/water dispensers) are some of the WORST causes of moisture issues in a kitchen. Most people think sinks or dishwashers, but the fridge is the worst...hands down. Pull the fridge out (put something under the feet and pull it forward. Remember to shut off water lines and unplug if you have to. That little bit of dark in the wood is hiding a much bigger issue. The sooner you get on this, the less damage you will have. Once you have found the leak, get in there with towels and fans and then call your home insurance to get the name of a remediation company. If you can see the floor from underneath (like a basement with an unfinished ceiling) then go ahead and do that after you make all the phone calls. Gravity LOVES to pull water DOWN. Only when water has backed up enough to create a little pond or reservoir will it move 'up' to the surface of a floor (like yours is doing).

What kind of grow medium is it in, and did you make sure it had an 'extra' measure of water to carry it over while you were away? It looks like oedema/ edema, a physiological disorder. Something I wrote about it: Oedema Oedema (aka edema) is a physiological disorder that can affect all terrestrial plants. It occurs when the plant takes up more water than it can rid itself of via the process of transpiration. The word itself means 'swelling', which is usually the first symptom, and comes in the form of pale blisters or water-filled bumps on foliage. Under a variety of circumstances/cultural conditions, a plant's internal water pressure (turgidity) can become so high that some leaf cells rupture and leak their contents into inter-cellular spaces in leaf tissue, creating wet or weepy areas. Symptoms vary by plant, but as the malady progresses, areas of the leaf turn yellow, brown, brown with reddish overtones or even black, with older damage appearing as corky/ scaly/ ridged patches, or wart/gall-like bumpy growth. Symptoms are seen more frequently in plants that are fleshy, are usually more pronounced on the underside of leaves, and older/lower leaves are more likely to be affected than younger/upper leaves. Oedema is most common in houseplants during the winter/early spring months, is driven primarily by excessive water retention in the soil, and can be intensified via several additional cultural influences. Cool temperatures, high humidity levels, low light conditions, or partial defoliation can individually or collectively act to intensify the problem, as can anything else that slows transpiration. Nutritional deficiencies of Ca and Mg are also known contributors to the malady. Some things that can help you prevent oedema: * Increase light levels and temperature * Monitor water needs carefully – avoid over-watering. I'd heartily recommend a soil with drainage so sharp (fast) that when you to water to beyond the saturation point you needn't worry about prolonged periods of soil saturation wrecking root health/function. Your soil choice should be a key that unlocks the solutions to many potential problems. * Avoid misting or getting water on foliage. It slows transpiration and increases turgidity. * Water as soon as you get up in the AM. When stomata close in preparation for the dark cycle, turgidity builds. If you water early in the day, it gives the plant an opportunity to remove (for its own needs) some of the excess water in the soil. * Put a fan in the room or otherwise increase air flow/circulation. Avoid over-crowding your plants. Al

Possibly an adult sawfly, if so then harmful, but only to certain plants especially roses.