Before I get into the critique, I'll answer your question about line weight. It always comes down to asking yourself what you're trying to achieve with the use of a certain tool, and understanding what a given tool is really intended to be used for. In the case of line weight, it does indeed have a specific purpose. It is to clarify the overlaps between forms in specific, localized areas. That means we're not tracing back over long areas of existing lines. The marks we add for line weight are themselves by design going to be short and are going to follow a simple, consistent trajectory. This goes hand in hand with the simple fact that we should be executing them confidently, using the ghosting method just as we would for the original linework. While this will make your accuracy suffer somewhat initially, remember that every drawing is an exercise, and if you mess up your line weight a bit it's not a big deal. These drawings are where you make your mistakes.

So, getting onto the homework, let's start with your organic forms with contour curves. These are generally looking good, save for one thing - it seems that while you are definitely making an effort to stick to the characteristics of simple sausages, you have a bit of a tendency to have some of their ends get stretched out, creating more of an ovoid rather than circular end. Watch out for that.

Continuing onto your insect constructions, for the most part you are doing a good job, and I am pleased to see the way in which you're building things up through the use of simple forms and defining their intersections with one another, but there are some issues I want to draw your attention to.

Firstly, because we're drawing on a flat piece of paper, we have a lot of freedom to make whatever marks we choose - it just so happens that the majority of those marks will contradict the illusion you're trying to create and remind the viewer that they're just looking at a series of lines on a flat piece of paper. In order to avoid this and stick only to the marks that reinforce the illusion we're creating, we can force ourselves to adhere to certain rules as we build up our constructions. Rules that respect the solidity of our construction.

For example - once you've put a form down on the page, do not attempt to alter its silhouette. Its silhouette is just a shape on the page which represents the form we're drawing, but its connection to that form is entirely based on its current shape. If you change that shape, you won't alter the form it represents - you'll just break the connection, leaving yourself with a flat shape. We can see this most easily in this example of what happens when we cut back into the silhouette of a form.

Now in your drawings, this is something we see in various places, but not always in really big, obvious ways. If we look at your mantidfly, there's a lot of this around the segments of your legs, where you're making little tweaks and refinements. It's definitely there in your tarantula as well, where you've drawn really big ball forms, but then largely ignored them and cut back into their silhouettes. Lastly, if you take a look at your ant's jaws, it's there in a few places - you're cutting back into the head, but what I want to draw your attention to here are the mandibles. The little jagged ends were basically just extended in 2D space, rather than 3D.

Instead, whenever we want to build upon our construction or change something, we can do so by introducing new 3D forms to the structure, and by establishing how those forms either connect or relate to what's already present in our 3D scene. We can do this either by defining the intersection between them with contour lines (like in lesson 2's form intersections exercise), or by wrapping the silhouette of the new form around the existing structure as shown here.

You can see this in practice in this beetle horn demo, as well as in this ant head demo.

This is all part of accepting that everything we draw is 3D, and therefore needs to be treated as such in order for the viewer to believe in that lie.

Now overall I'm still pretty happy with the general trend of your work. You are showing that you're thinking in 3D space in a lot of places, even if it's not always as consistent as it could be. Looking at the monkey hopper's abdomen, you've done a great job of wrapping the segmentation around the base structure. With the longhorn beetle, the way you've constructed the head - specifically its mandibles - is pretty good as well (though definitely be sure to draw every form in its entirety, even where they overlap existing forms).

The last thing I wanted to call out is just that while you are making a concerted effort to use the sausage method for your leg constructions, and it's clear that you're building upon those structures (which is great to see), here you can see ways to approach building up that structure additively. The key is to make lots of contact with the existing structure - so instead of enveloping a form, we wrap individual pieces around it, creating a more believable, solid result. You can also see this concept at play here, as well as in this ant leg demo and even in this dog leg.

So! Overall, you're doing well, but you do have some areas to work on. Fortunately, they are all equally relevant throughout the next lesson, so I'll leave you to it. You can consider this lesson complete.