Mottled boleteLeccinum variicolor

Yes. The multicolored reaction when cut is a normal trait of the species, part of its name. It's oxidation of pigments, not a sign of toxicity. Birch boletes have no dangerous lookalikes among boletes at all.

The bitter bolete (Tylopilus felleus) has a dark network on the stem (not scales) and a plain, not spotted, cap. Its flesh turns strongly pink and has an unbearably bitter taste. In the mottled bolete, the scales on the stem and the spots on the cap are the telltale features.

In birch woods and mixed forests with birch, less often with oak, poplar or spruce. It likes damp microhabitats — hollows, the edges of wet ravines, the shores of forest lakes. Polissia, the Western Forest-Steppe and the Carpathians are its main range.

From June to October, peaking in August–September after heavy rains. In very dry years it's rare. It likes moderately warm, humid weather after prolonged rain.

The main difference is the spotted “camouflage” cap (the brown birch bolete's is evenly gray or brown). Second, the multicolored flesh when cut (in the brown birch bolete it's white or turns slightly pink only in the stem). The scales on the stem are similar.

The red-capped scaber stalk has a bright orange or red cap (no spots), and its flesh turns blue when cut. The mottled bolete is darker, with distinctive spots, and its flesh shows a mixed reaction. Both are edible, so no harm done.

Yes, like all birch boletes — especially in warm weather. So pick only young, firm specimens with closed pores. Old mushrooms with open gray pores are usually already wormy.

Drying, pickling, freezing. Dried, it darkens more than porcini but keeps its aroma. It pickles well and holds its shape. Before pickling, parboil for 15–20 min and discard the first water.